Question

If the sum of q terms of an AP is 63q - 3q^2 and the pth term is -60, find value of p

Answer 1

Hey


Given that :-

♦ Sum of q terms

= 63q - 3q²

Let q = 1 ,

then ,

63 ( 1 ) - 3 ( 1 ) ²

= 63 - 3

= 63 .

So , term 1 = 63

Now , let q = 2

63 ( 2 ) - 3 ( 2 ) ²

= 126 - 12

= 114 .

Sum of term1 and term2 = 114

So,

t1 + t2 = 114

=> 60 + t2 = 114

=> t2 = 114 - 60

=> t2 = 54 .

So , a = 60 , d = ( - 6 ) .

And also ,

pth term = ( - 60 )

So ,

a + ( p - 1 ) d = - 60

=> 60 + ( p - 1 ) ( - 6 ) = -60

=> ( p - 1 ) ( - 6 ) = - 120

=>. p - 1 = 20

=> p = 21 .

thanks :)