Question

Find the no. Of terms of an ap whose third term os 20 ,8th term is 10 and the sum of terms is 144.Explain the double answer

Answer 1

A/Q

a+2d=20....i

and a+7d=10.....ii

ii-i gives

5d=-10

d=-2

therefore

a=24

and

n/2(2a+(n-1)d)=144

48n-2n^2+2n=288

2n^2-50n+288=0

n^2-25n+144=0

n^2-(16n+9n)+144=0

n(n-16)-9(n-16)=0

n=9 or =16

Ans =

No of terms =16

MARK BRAINLIEST

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