Large numbers begone

Algebra Level 2

Evaluate

12 3 3 + 45 6 3 12 3 2 123 × 456 + 45 6 2 . \frac{ 123^3 + 456^3 } { 123^2 - 123 \times 456 + 456 ^2 }.


The answer is 579.

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15 solutions

Prasun Biswas
Dec 20, 2013

Just split the numerator using the identity ( a 3 + b 3 ) = ( a + b ) ( a 2 a b + b 2 ) (a^{3}+b^{3})=(a+b)(a^{2}-ab+b^{2})

= ( 12 3 3 + 45 6 3 ) ( 12 3 2 123 × 456 + 45 6 2 ) =\frac{(123^{3}+456^{3})}{(123^{2}-123\times 456+456^{2})}

= ( 123 + 456 ) ( 12 3 2 123 × 456 + 45 6 2 ) ( 12 3 2 123 × 456 + 45 6 2 ) =\frac{(123+456)(123^{2}-123\times 456+456^{2})}{(123^{2}-123\times 456+456^{2})}

= ( 123 + 456 ) = 579 =(123+456) = \boxed{579}

Nicely solved !

Devesh Rai - 7 years, 5 months ago

Nice

Low Wei Chian - 7 years, 5 months ago

Very Nice..!!

Ajinkya Mohadkar - 7 years, 5 months ago

brilliant attack

sathiya narayanan - 7 years, 5 months ago

nice boss very well

Vinod Makwana - 7 years, 5 months ago

very well done

Fahim Bakhtier - 7 years, 5 months ago

nice one!

Iyvon Teh - 7 years, 5 months ago

nice

danish khaleeq - 7 years, 5 months ago

good!!!

TIRTHANKAR GHOSH - 7 years, 1 month ago

This question can be solved by using an algebraic identity i.e. a 3 + b 3 = ( a + b ) ( a 2 a b + b 2 ) a^{3}+b^{3}=(a+b)(a^{2}-ab+b^{2}) Let a = 123 a=123 and b = 456 b=456 Now, let's solve the equation, a 3 + b 3 a 2 a b + b 2 \frac{a^{3}+b^{3}}{a^{2}-ab+b^{2}} = ( a + b ) ( a 2 a b + b 2 ) a 2 a b + b 2 =\frac{(a+b)(a^{2}-ab+b^{2})}{a^{2}-ab+b^{2}} = a + b =a+b Substituting the values of a a and b b , we get, a + b a+b = 123 + 456 =123+456 = 579 =\boxed{579}

Hùng Minh
Dec 20, 2013

123^3 + 456^3 = (123 + 456)(123^2−123×456+456^2) <=> The result is 123 + 456 = 579

Aditya Adi
Dec 19, 2013

Using formulae a3+b3/(a2-a.b+b2)

apply the factorization in the numerator

Rich Belen - 7 years, 5 months ago

No ! ! It's much simpler Remember this identity ........ :- a^{3} + b^{3} = (a+b) (a^{2} + b^{2} - ab)

by this we get :- (123 + 456 ) ( 123^{2} - 123 x 456 + 456^{2} )
/ ( 123^{2} - 123 x 456 + 456^{2} )

therefore we get , 123 + 456 = 579

Rohitas Bansal - 7 years, 5 months ago

Could you write how you did it.

Soham Dibyachintan - 7 years, 5 months ago

Log in to reply

refer rohitas bansal

sathiya narayanan - 7 years, 5 months ago
Tunk-Fey Ariawan
Feb 2, 2014

Take a look this simple trick: ( x 3 + y 3 ) = ( x + y ) ( x 2 x y + y 2 ) , (x^3+y^3)=(x+y)(x^2-xy+y^2), then x 3 + y 3 x 2 x y + y 2 = x + y . \frac{x^3+y^3}{x^2-xy+y^2}=x+y. Now, let x = 123 \,x=123\, and y = 456 \,y=456 . Therefore 12 3 3 + 45 6 3 12 3 2 ( 123 ) ( 456 ) + 45 6 2 = 123 + 456 = 579 \frac{123^3+456^3}{123^2-(123)(456)+456^2}=123+456=\boxed{579} # Q . E . D . # \text{\# }\mathbb{Q}.\mathbb{E}.\mathbb{D}.\text{\#}

Saurabh Mallik
Apr 18, 2014

We can solve this question using algebraic identity:

( a 3 + b 3 ) = ( a + b ) ( a 2 a b + b 2 ) (a^{3}+b^{3})=(a+b)(a^{2}-ab+b^{2})

Let a = 123 a = 123 and b = 456 b=456 . So,

( a 3 + b 3 ) ( a 2 a b + b 2 ) = ( 12 3 3 + 45 6 3 ) ( 12 3 2 123 × 456 + 45 6 2 ) \frac{(a^{3}+b^{3})}{(a^{2}-ab+b^{2})}=\frac{(123^{3}+456^{3})}{(123^{2}-123 \times 456+456^{2})}

= ( 123 + 456 ) ( 12 3 2 123 × 456 + 45 6 2 ) ( 12 3 2 123 × 456 + 45 6 2 ) = \frac{(123+456)(123^{2}-123 \times 456+456^{2})}{(123^{2}-123 \times 456+456^{2})}

= 123 + 456 = 579 =123+456=579

Thus, the answer is 579 \boxed{579}

Muzzammal Alfath
Dec 24, 2013

123^3+456^3/123^2-123 456+456^2=(123+456)(123^2+456^2-123 456)/(123^2+456^2-123*456)=123+456=579

Maria Felicita
Dec 24, 2013

The first step is you know that all of them is seem likely and you must simplify it

First

[[\frac{ ( 123 + 456 ) 3 (123+456)^{3} -3 × \times 123 × \times 456(123+456)}{ ( 123 + 456 ) 2 (123+456)^{2} - 3 × \times 123 × \times 456 ]]

Second pull out the (123+456)

[[\frac{(123+456) ( 123 + 456 ) 2 (123+456)^{2} - 3 × \times 123 × \times 456}{ ( 123 + 456 ) 2 (123+456)^{2} - 3 × \times 123 × \times 456}]]

Then you can remove it and this the answer

123 + 456 = 579 \boxed{123+456 = 579}

Jatin Valecha
Dec 22, 2013

123+456=579 { use (x^3+y^3)/x^2-xy+y^2) = x+y

Shiv Gaur
Dec 22, 2013

Use the identity 123^3 + 456^3 =(123+456) (123^2-123*456 +456^2) So you are left with 123+456 in the numerator which equals 579.

Tanmoy Tk
Dec 20, 2013

=(123+456)(123^2-123 456+456^2)/(123^2-123 456+456^2) =123+456 =579

Arafat Asim Riyad
Dec 20, 2013

BREAK THE ABOVE QUBE LAW & AVOID THE SAME THING.THEN ANS IS:123+456=579

(a^{3}+b^{3})=(a+b)(a^{2}-ab+b^{2}) is one of the formaulas i.e.
( a^{3}+b^{3} ) / ((a^{2}-ab+b^{2}) = (a+b)

when you put a=123 and b=456 you get the above expression which is equivalent to a+b i.e 123+456 i.e. 579

123^{3}+456^{3}/123^{2}-123 456+456^{2} =(123+456)(123^{2}-123 456+456^{2})/(123^{2}-123*456+456^{2}) =123+456 =579

Ajay Maity
Dec 20, 2013

The formula for a 3 + b 3 a^{3} + b^{3} is ( a + b ) ( a 2 a b + b 2 (a + b)(a^{2} - ab + b^{2}

Apply the same in the numerator,

( 123 + 456 ) ( 12 3 2 123 × 456 + 45 6 2 ) ( 12 3 2 123 × 456 + 45 6 2 ) \frac{(123 + 456)(123^{2} - 123 \times 456 + 456^{2})}{(123^{2} - 123 \times 456 + 456^{2})}

= 123 + 456 = 123 + 456

= 579 = 579

That's the answer!

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