Why are all the answers still so large?

Algebra Level 1

3 1506 3 1505 = ? \large \color{#D61F06}3^{\color{#3D99F6}{1506}} - \color{#D61F06}3^{\color{#3D99F6}{1505}} = \ ?

3 3 3 1505 3^{1505} 6 × 3 1504 6 \times 3^{1504} 3 × 1505 3 \times 1505

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46 solutions

Dpk ­
Jul 25, 2014

To make it easier to visualize I let x = 3 1505 . x = { 3 }^{ 1505 }. This means that 3 x = 3 1506 . 3x = { 3 }^{ 1506 }. Therefore, the given expression becomes 3 x x = 2 x . 3x - x = 2x. Now, substitute our value of x x back in to obtain ( 2 ) ( 3 1505 ) . (2)({ 3 }^{ 1505 }). However, since that is not in the choices, we factor out another 3 3 from 3 1505 { 3 }^{ 1505 } like so:

( 2 ) ( 3 ) ( 3 1504 ) = ( 6 ) ( 3 1504 ) = 6 × 3 1504 (2)(3)({ 3 }^{ 1504 }) = (6)({ 3 }^{ 1504 }) = \boxed { 6 \times { 3 }^{ 1504 } }

Just take 3 1504 3^{1504} common.

Snehal Shekatkar - 6 years, 10 months ago

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can you tell me further

Kango Reihan - 6 years, 10 months ago

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3 1506 3 1505 = 3 1504 ( 3 2 3 ) = 3 1504 ( 9 3 ) = 6 3 1504 3^{1506} - 3^{1505} = 3^{1504} (3^{2} - 3) = 3^{1504}(9 - 3) = 6 * 3^{1504}

Haidar Abboud - 6 years, 10 months ago

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@Haidar Abboud The simplest solution. I had hard time understanding the solution posted by dpk

RJ Ambrocio - 5 years, 9 months ago

@Haidar Abboud Wow, this is so simple and clear explanation.. Thx,

Novice Ayu Abrianti - 5 years, 9 months ago

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@Novice Ayu Abrianti What is wrong with 2×3*1505

Chirayathmanjiyil Paul - 4 years, 11 months ago

@Novice Ayu Abrianti Yes, is so simple. great!

Rohmah Nur Fitriana - 5 years, 6 months ago

@Haidar Abboud that's really a simply way...

mmr raju - 5 years, 2 months ago

@Haidar Abboud Good solution

Alaa El-din Solaiman - 5 years ago

@Haidar Abboud this solution is so simple, thanks!

robi joy tan - 6 years, 6 months ago

@Haidar Abboud wow!!! that's great, explaination..

Lalit Sunar - 5 years, 10 months ago

@Haidar Abboud Why is it 1504 as the common? I want to know

Jayi Enad - 5 years, 9 months ago

There is a little, little bit of a problem here since it seems like you have already assumed that you're going to take the (6)(3^1504) as your choice for the answer, that's why you took 3^1504 as its common. It isn't wrong but... I don't know... :3 Anyways, my solution was very much the same with sir Dpk so...

Wolfred Moonlake - 5 years, 10 months ago

simple and easy solution, nice!

Jason Gacrama - 6 years, 10 months ago

common factor is 3^1505. so the expression becomes: 3^1505 x (3-1) or 3^1505 x (2). but 3^1505 = 3^1504 x 3. so the expression is now: 3^1504 x 3 x 2 or 6 x 3^1504.

Binong Taft - 6 years, 10 months ago

Thank you for this great solution!

Ahmed Ali - 5 years, 10 months ago

the best and easy solution

Adithya Bvn - 6 years, 10 months ago

Very nicely explained,Congratulations!!!

Krishna Garg - 5 years, 11 months ago

a moment of silence for those who did this wrong!! :P :P

A Former Brilliant Member - 5 years, 9 months ago

why it becomes 3x? can we assume it with any number? the x one i understood. and the final answer is been factorise? overall smart solution!

Nurhamizah Rashid - 6 years, 10 months ago

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see dear, 3^1506=3^1505 3 so if 3^1505=x then 3^1506= 3 3^1505=3x

Anirban Chowdhury - 6 years, 10 months ago

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i hope i am able to clear ur doubts

Anirban Chowdhury - 6 years, 10 months ago

This solution is correct

Mohamed Helal - 6 years, 10 months ago

The answers to this questions I have seen are very long winded, when you can just use log and get the answer.

Shamari Robinson - 6 years, 10 months ago

This is very nicely explained by Dpk Philippines,Congratulations!!!

Krishna Garg - 5 years, 11 months ago

where do u get the 2x? :(

James Gomes - 5 years, 7 months ago

I just loved the way of solutioion😊

নির্জন মেঘ - 5 years, 5 months ago

I'd like to ask, why does 12^{3} - 10^{3} = 728 ? I need the solutions. Thanks in advance

yessy yosephine - 6 years, 8 months ago

Awesome explanation

Rohan Bobby - 5 years, 8 months ago

can you tell me clearly?

maryam akram - 6 years, 10 months ago

answer is 1

Abdulrahman Shaat - 6 years, 10 months ago

if 3^3-3^2=3 Therefore 3^1506-3^1505=3 isn't it?

Kandarp Kakkad - 6 years ago

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No dude...you can substract that way with square only when there is a divide sign.. in case of multiplication you add.. here its a minus sign so that you cant do.. sorry

Kaushlya Bhavsar - 6 years ago

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ty vvm for the guidance

Kandarp Kakkad - 6 years ago

what if we take Log of the eq Log(3^1506-3^1505)----->> Log(3^1506/3^1505) ----->> Log(3) [Ans]

Sohaib Pakistanii - 6 years, 10 months ago

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We have a formula for l o g n A B = l o g n A l o g n B log_n\frac{A}{B} = log_n A - log_n B . However, l o g n ( A B ) l o g n A B log_n (A - B) \neq log_n\frac{A}{B} .

Datu Oen - 6 years, 9 months ago

is this a child's math,, every one know that it can be written as 6x3^1504 .

Or my result is this,

(6)(1.85302019E+15)^47

But what is the actuall answer.

Rahul Sharma - 6 years, 10 months ago
Hassan Raza
Jul 30, 2014

3 1506 3 1605 = 3 1605 × 3 3 1605 T a k e " 3 1605 " c o m m o n = 3 1605 ( 3 1 ) = 3 1605 ( 2 ) = ( 2 ) ( 3 ) 3 1604 = 6 × 3 1604 \quad { \quad 3 }^{ 1506 }-{ 3 }^{ 1605 }\\ =\quad { 3 }^{ 1605 }\times 3-{ 3 }^{ 1605 }\quad \quad \quad Take\quad "{ 3 }^{ 1605 }"\quad common\\ =\quad { 3 }^{ 1605 }(3-1)\\ =\quad { 3 }^{ 1605 }(2)=(2)(3){ 3 }^{ 1604 }\\ =\quad 6\times { 3 }^{ 1604 }

you made mistake in your solution ... :P

Muhammad Ahtesham Anwer - 6 years, 10 months ago

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What mistake that I made?

Hassan Raza - 6 years, 10 months ago

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You have done mistake in taking power there is 1505 and you have taken as 1605 but very good solution

Amit Mishra - 5 years, 9 months ago

what if we take Log of the eq Log(3^1506-3^1505)----->> Log(3^1506/3^1505) ----->> Log(3) [Ans]

Sohaib Pakistanii - 6 years, 10 months ago

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I think I did well. Is it?

Hassan Raza - 6 years, 10 months ago

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it was just the manner of writing..instead of the exponent 1506, what you had is 1605..

Joseph Belida - 6 years, 10 months ago

The factorization are not the same..

Jeo Silvano - 6 years, 10 months ago

The question u wrote and solved is wrong.

Sahba Hasan - 6 years, 7 months ago
Finn Hulse
Jul 27, 2014

Because this is a multiple choice, parity is a valid option. Notice how both 3 1506 3^{1506} and 3 1505 3^{1505} are odd. Their difference is even. Because of this, there will be a 2 2 somewhere in the factorization. The only even option choice is 6 × 3 1504 \boxed{6 \times 3^{1504}} .

well done even though the normal solution wasn't that difficult or lengthy, parity is something i always commend :)

Aman Chandila - 6 years, 10 months ago

True. The options 3 and 3*3105 are dismissed easily. But calculation does help prove the answer.

Therverson Kanavathy - 6 years, 10 months ago

what if we go by this way?? take the power 1506 as x... then the power 1505 comes as (x-1)... then by equating we get 3^(x-x+1)... which in turn comes as 3^1.. which is 3... what's say?? can we proceed like dis???

Indradeep Bhattacharya - 6 years, 10 months ago

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of course not. From where you the idea of 3^(x-x+1)??

Alviando Hendriawan - 6 years ago
Kathakali Mitra
Jul 5, 2015

Sol: 3^1506 - 3^1505

= 3^1505 × 3^1 - 3^1505

= 3^1505(3^1-1)

= 3^1505(2)

= 3×3^1504×2

= 6×3^1504

Jason Carr
Jul 27, 2014

Here's the logic I used to originally make this problem;

First I took the base formula of 3 n 3 n 1 3^{n} - 3^{n-1} , where n is greater than or equal to 2. I started with the first three possible solutions

3 2 3 1 = 9 3 = 6 3^{2} - 3^{1} = 9 - 3 = 6

3 3 3 2 = 27 9 = 18 3^{3} - 3^{2} = 27 - 9 = 18

3 4 3 3 = 81 27 = 54 3^{4} - 3^{3} = 81 - 27 = 54

It was here that I saw that the answer to each of these was divisible by 3, so...

6 / 3 = 2 6 / 3 = 2

18 / 3 = 6 18 / 3 = 6

54 / 3 = 18 54 / 3 = 18

This one took me a bit longer to figure out. I saw that the last two were once again multiples of 3, but the 2 threw me off. Until I remembered that any number to the power of 0 is equal to 1. Thus...

2 = 2 x 3 0 2 = 2 x 3^{0}

6 = 2 x 3 1 6 = 2 x 3^{1}

18 = 2 x 3 2 18 = 2 x 3^{2}

As I had already divided the original answers by 3, all I had to do was multiply the above information by 3 to find the solution. So

3 n 3 n 1 = 6 x 3 n 2 3^{n} - 3^{n-1} = 6 x 3^{n-2}

To verify my work, I used my formula to calculate answers up to n = 10. I do apologize if the work and explanation is crude. I'm not mathematician, merely a guy that really likes math.

In hindsight though, I do believe that while I initially assumed n had to be >= to 2, I believe that it can be any integer. I did the math up to n = -9 and each time it worked out.

can any one help me understand that how 6 comes

Kango Reihan - 6 years, 10 months ago

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by writing 3^1505 as 3*3^1504 and then multiplying 2 and3

Shrinivas Pai - 6 years, 10 months ago

@Tasaduq Soomro help me on this problm

Kango Reihan - 6 years, 10 months ago

this is just but a sample problem on how the principle of mathematical induction can be applied to conclude divisibility by 3...

Joseph Belida - 6 years, 10 months ago
Amar Ashish
Aug 1, 2014

just take 3^1504 common from equation then it will become 3^1504(3^2-3^1) so,3^1504(9-3) so answer will be 6*3^1504

3^1506-3^1505= 3 (3^1505)-3^1505=(3^1505) (3-1)=2 (3^1505)=2 3 (3^1504)=6 (3^1504)

Betty BellaItalia
Dec 30, 2017

3 1506 3 1505 \large 3^{1506}-3^{1505}

= 3 ( 3 1505 3 1505 \large =3(3^{1505}-3^{1505}

= 3 1505 ( 3 1 ) \large =3^{1505}(3-1)

= 2 × 3 1505 \large =2 \times 3^{1505}

= 2 ( 3 ) ( 3 1504 ) \large =2(3)(3^{1504})

= 6 × 3 1504 \large =6 \times 3^{1504}

Anshu Garg
Nov 12, 2016

3 1506 3 1505 3^{1506}-3^{1505} = 3 1505 [ 3 1 ] 3^{1505}[3-1] = 3 1505 [ 2 ] 3^{1505}[2] = 6 [ 3 1504 ] 6[3^{1504}]

Pranay Devidan
Sep 16, 2016

3^1506 - 3^1505

=3^1505 ( 3 - 1 )

=3 * 3^1504 ( 2 )

=6 * 3^1504

Mit 0910
Jun 13, 2016

I think it is a lot easier to factor out 3^1505 and write the answer as 3^1505 (3-1) = 3^1505 (2)

3^1506-3^1505=3 3^1505-3^1505=3^1505(3-1)=2 3^1505=6*3^1504

Alan Hc
Mar 12, 2016

Krishna Chaitu
Nov 18, 2015

Take 3^1505 as common it implies 3^1506 - 3^1505=3^1505(3-1) =6×(3^1504)

Caroline Lui
Nov 17, 2015

Just the way I thought about it: 3^1506 is 3^1505 X 3, so factoring out the 3^1505 you get 2 x 3^1505, which can be converted into 6 x 3^1504

Best so far

Thomas Quin - 4 years ago
Mohammed ElMagico
Nov 15, 2015

3^1506-3^1505=3^1505(3-1) =3^1504 * 3 * 2=6*3^1504

Samwail Siddiqui
Oct 30, 2015

Taking out 3^1505 common we ve: 3^1505(3-1) =3^1505(2) . Again taking out 3 as common we ve 3 (3^1504) 2= 6*3^1504

Atika Samiha
Oct 29, 2015

3^1505x(3-1) =2x3^1505 =6x3^1504

Gouri Asnani
Oct 8, 2015

3^1506-3^1505=(3^1504 3^2 )-(3^1504 3^1)=3^1504 (3^2 -3)=3^1504 (9-3)=3^1504*6

Phak Mi Uph
Oct 6, 2015

3^{1506} - 3^{1505}

=3^{1505}(3-1)

=3^{1505} * 2

=3 * 3^{1504} * 2

=3 * 2 * 3^{1504}

= 6 * 3^{1504}

David Hall
Sep 11, 2015

3^1506 - 3^1505 = 3 * 3^1505 - 3^1505 = 2 * 3^1505 = 2 * 3 * 3^1504 = 6 * 3^1504

Answer: 6 * 3^1504

Sandip Gawali
Aug 5, 2015

[(3^1505) x 3 - 3^1505] =[3^1505][3-1] =[3^1505][2] =[(3^1504) x 3][2] =6 x 3^1504

Krishna Bhati
Jul 24, 2015

3^1505( 3-1) = 3^1505 * 2 3^1504 2 3 = 3^1504 *6

Somesh Kushwaha
Jul 23, 2015

3^1506 - 3^1505 = 3^1505(3-1)

                                         =   3^1505 * 2


                                         =  3*2*3^1504


                                        = 6*3^1504
Hadia Qadir
Jul 23, 2015

Sol: 3^1506 - 3^1505 = 3^1505 × 3^1 - 3^1505 = 3^1505(3^1-1) = 3^1505(2) = 3×3^1504×2 = 6×3^1504

Naveen Reddy
Jul 23, 2015

use basic principle of algebra: a^m*a^n=a^(m+n)

Ameya Patil
Jul 23, 2015

just form a series of...

3^1 - 3 ^0 = 2 3^2 - 3^1 = 6 3^3 - 3^2 = 18 3^4- 3^3 = 54.....................................and so on...

check the options .... now,

2 can be written as...... 6 x 3^(-1) 6 can be written as ..... 6x 3^(0) 18 can be written as ... 6 x 3^(1)... so the only option that satisfies this form is ...

      6 x 3^(1504)....hahahahahahaha
Anjali Bhati
Jul 23, 2015

Simply take 3^1505 common. Then the equation becomes as: => 3^1505(3^1-1) => 3^1505(2) Again take a 3^1 out of 3^1505 as: => 3^1504(3^1×2) =6×3^1504 is the required answer! ☺

Victor Sebastian
Jul 10, 2015

Its simple..just take out the second term common and solve

Mahmoud Elshazly
Jun 18, 2015

The key is to take a common factor of 3^1505...

Musheer Uzzaman
Jun 1, 2015

There are so many terms that can be taken as common. But according to the given options,

we will take 3^1504 common

then the solution will be 6×(3^1504)

3 1506 3^{1506} - 3 1505 3^{1505} = ?

3 × 3 1505 3\times3^{1505} - 1 × 3 1505 1\times3^{1505} = 2 × 3 1505 2\times3^{1505}

Rewriting 2 × 3 1505 2\times3^{1505} = 2 × 3 × 3 1504 2\times3\times 3^{1504} or 6 × 3 1504 6\times3^{1504}

Aravind Vishnu
Jan 7, 2015

taking 3^1505 common, we get the expression as 2(3^1505) which is the same as 6x3^1504

Garvin Goei
Jan 4, 2015

Actually the answer is 2 x 3^1505; but since it doesn't appear in the answer choices, the answer is 6 x 3^1504.

How to find it?

3^1506 - 3^1505

changes the 3^1506 into 3 x 3^1505: 3 x 3^1505 - 3^1505

then: 3^1505(3-1)

then 3^1505 x 2

then changes 3^1505 into 3 x 3^1504 3 x 3^1504 x 2

then: 6 x 3^1504

Dorian Thiessen
Aug 24, 2014

As we can see by playing around, any power of three subtract three to a power one less is just two times that last power of three.

3^2 - 3^1 = 6 = 2 * 3^1

and...

3^3 - 3^2 = 18 = 2 * 3^2

Generally:

3^(x) - 3^(x-1) = 2 * 3^(x-1)

Take out one factor of three on the RHS and we get one of the possible answers:

2 * 3^(x-1) = 6 * 3^(x-2)

Specifically:

3^1506 - 3^ 1505 = 6 * 3^1504

Akshay Kumar
Aug 20, 2014

taking 3^1505 as a common factor we get 3^1505(3-1) which is equal to 3^1505 2=3^1504 3 2=6 3^1504

Vinay Myakala
Aug 19, 2014

3^1506 - 3^1505= 3^1505(3-1)= 3^1505(2)= 3^1504 * 3 * 2= 6 * 3^1504

9 - 3 = 6, 6 = 2 x 3

27 - 9 = 18, 18 = 2 x 9

...

243 - 81 = 162, 162 = 2 x 81

Then ...

3 1506 3 1505 = 2 x 3 1505 3^{1506} - 3^{1505} = 2 x 3^{1505}

2 x 3 1505 = 2 x 3 x 3 1504 = 6 x 3 1504 2 x 3^{1505} = 2 x 3 x 3^{1504} = 6 x 3^{1504}

Mohammad Iqbal
Aug 18, 2014

The same is 3^1505 so we can write 3^1505(3^1-3^0) =3^1505x2 or 6x3^1504. Simple man !

Pigeon Gymnastic
Aug 18, 2014

Using Tn = ar^(n-1)

3^1506 - 3^1505 = 3(3^1505)-3^1505 = 2(3^ 1505)= 2 (3^1054) x3 = 6 (3^1504)

Suraj Lal
Aug 14, 2014

3^1505(3-1)

=2*3^1505

=2 3 3^1504

=6*3^1504

Lu Chee Ket
Aug 4, 2014

2.3362448054767730667041342431036e+718

Shrinivas Pai
Jul 31, 2014

just take out the common. its just like child's play

Saquib Rahman
Jul 30, 2014

3^{1506} – 3^{1505} = 3^{1505} (3 – 1) = 2 \times 3^{1505} = 2 \times 3 \times 3^{1504} = 6 \times 3^{1504}

3^1506 - 3^1505 = 3×3^1505 - 3^1505 = 3^1505(3 - 1) =2 × 3^1505

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