Question

How many terms of the sequence -12,-9,-6,-3,.......must be taken to make the sum 54?​

Answer 1

Question :

How many terms of the sequence -12,-9,-6,-3,.......must be taken to make the sum 54?

Answer :

As per the data given ,

First term = a = - 12

Common difference = d = -9 - (-12) = 3

Sum = s = 54

Number of terms = n = ??

In an Arithmetic sequence ,

Sum (s) = [n/2 (2a + (n-1) d )]

substitute the values known to find the unknown value " n " .

54 = [n/2 (2 × -12 + (n-1) -3 )]

Solve this equation for the value of " n "

Value of n = 13..

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~ hope it helps :)

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