An algebra problem by Mihir Srivastava

Algebra Level 3

The Sum of the first n n terms of an A.P. is 5 n 2 + 3 n 5n^2+3n . If its m t h m^{th} term is 168 168 , find the value of m m .


The answer is 17.

Mihir Srivastava by Mihir Srivastava , 22, India

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3 solutions

Akagami Ng
Aug 2, 2014

answer answer

2 Helpful 0 Interesting 0 Brilliant 0 Confused
Hemang Sarkar
Jul 24, 2014

the mth term is 5m^2 + 3m - 5(m-1)^2 -3(m-1).

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awesome !!!!!!!!!

Mayank Holmes - 6 years, 10 months ago
Mudit Jha
Aug 2, 2014

The sum of n terms of an AP is given by: S = n/2 { 2a + (n-1)d } Here, sum of first n terms is 5n^2 + 3n. By bringing both the equations to a similar form and comparing the coefficients, it can be seen that a = 8 and d= 10. Now 168 is the mth term, Hence a + ( n -1)d = 168 where n is 17

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