Telescoping Series 2 – Future Terms

Algebra Level 2

Consider the following pattern:

1 1 × 2 = 1 1 1 2 1 2 × 3 = 1 2 1 3 1 3 × 4 = 1 3 1 4 \begin{aligned} \frac{1}{1\times 2} & = \frac{1}{1} - \frac{1}{2} \\ & \\ \frac{1}{2\times 3} & = \frac{1}{2} - \frac{1}{3} \\ & \\ \frac{1}{3\times 4} & = \frac{1}{3} - \frac{1}{4} \\ \vdots & \end{aligned}

Following the pattern above, if 1 11 × 12 = 1 a 1 b , \displaystyle \frac{1}{11\times 12} = \frac{1}{a} - \frac{1}{b}, what are the values of a a and b b ?

a = 12 a = 12 and b = 11 b = 11 a = 11 a = 11 and b = 10 b = 10 a = 11 a = 11 and b = 12 b = 12 a = 10 a = 10 and b = 11 b = 11

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16 solutions

The problem solve by this equation. {1/(n*(n+1))=(1/n)-(1/n+1)}

a=11& b=12

S.M.MOMENUL ISLAM - 7 years, 2 months ago

a=11 and b=12

Sabrine Asal - 7 years, 2 months ago

Log in to reply

how???

Abdullah Sh - 7 years, 2 months ago

a=11 and b=12

Jigyashu Dewangan - 7 years, 2 months ago

The problem can be solved by this equation. {1/(n*(n+1))=(1/n)-(1/n+1)}. Though this is not required because the theory and examples are given. But if they were not there then this equation is the best method.

Ashtik Mahapatra - 7 years, 2 months ago

a=11 and b=12

sumit mishra - 7 years, 2 months ago

a=11 n b=12

Nazmul Jewel - 7 years, 2 months ago

a = 11 , b=12

soni kamtam - 7 years, 2 months ago

a=11,b=12

Aditya Raj - 7 years, 2 months ago

a=11 & b=12

Hameer Rai - 7 years, 2 months ago

a=11& b=12

Lucreta Portal - 7 years, 2 months ago

a=11 and b=12

dwaipayan ROY - 7 years, 2 months ago

a=11 b=12

sohail daftri - 7 years, 2 months ago

a=11& b=12

Meghe Meghe Akashta - 7 years, 1 month ago

i solved it again

Armaan Das - 7 years, 1 month ago

see tipe

Imam Edogawa - 7 years, 1 month ago

So easy??????!!!!

Taiba Zaidi - 7 years, 1 month ago

a=11& b=12

Hanaa Ahmed - 7 years, 1 month ago

a=11 and b=12

ARSH RAJ - 7 years, 1 month ago

a = 11 and b = 12

Joyce Cagampang - 7 years, 2 months ago

it follows a logic so a=11 and b=12

a=11 and b=12

Mahdi Hasan - 7 years, 2 months ago

a=11, b=12

Marknell Sese - 7 years, 2 months ago

I think that 's right!

Thu Minh - 7 years, 2 months ago

a=11, b=12

Govind Choudhary B - 7 years, 1 month ago

Actually the series is a telescoping series which is a series where each term can be represented in the following way , u k = t k t k + 1 . . . . . . . . ( 1 ) u_{k} = t_{k} - t_{k+1} ........(1) Where t k t_{k} is some series.

For this series we can see that t k = 1 n t_{k} = \frac{1}{n} so u k = 1 n × ( n + 1 ) u_{k} = \frac{1}{n\times(n+1)}

so from (1) it can be seen that 1 n × ( n + 1 ) = 1 n 1 n + 1 \frac{1}{n\times(n+1)} = \frac{1}{n} - \frac{1}{n+1}

Fahim Khan
Apr 29, 2014

The theory is 1/n(n+1))=(1/n)-(1/n+1) and the the answer will be a = 11 and b = 12

Mahabubur Rahman
Apr 18, 2014

when 1/2-1/3 then a=2, b=3 this way 1/11-1/12 gets a=11 b=12

Sandeep Coorg
Apr 16, 2014

By observing the patter it is like a series with nth term 1/n-1/n+1

Amit Tomar
Apr 15, 2014

its very easy.......i simply looked at the denominator's pattern

Shaina Heyres
Apr 13, 2014

I actually just followed the patterns on the denominators.

by solving 1/11-1/12 we get result as 1/(11*12) so a=11& b=12

Prashant Patel
Apr 12, 2014

we know (1/n)-(1/(n+1)) = 1/(n*(n+1)) so in this case n = 11. so a=11 and b=12

Saahil Dhaka
Apr 11, 2014

same solution because the result has to be positive so the bigger fraction first

Gautam Basu
Apr 11, 2014

Follow the pattern. 1/n - 1/(n+1) = 1/n*(n+1)

Ashtik Mahapatra
Apr 11, 2014

The problem can be solved by this equation. {1/(n*(n+1))=(1/n)-(1/n+1)}. Though this is not required because the theory and examples are given. But if they were not there then this equation is the best method.

Connor Kenway
Apr 10, 2014

this problem should have been there without all that theory and examples thers nothing to do just write 1 as 12-11 and cancel

Abid Ali
Apr 9, 2014

1/11- 1/12 ,shows a=11 and b=12 Ans

easy to solve. good

Sushma Vashisht - 7 years, 2 months ago
Krishna Garg
Apr 9, 2014

similar to given details, 1/11- 1/12 ,shows a=11 and b=12 Ans

K.K.GARG,India

a=11 and b=12

takya momena - 7 years, 2 months ago

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