Question

How many terms of the A.P 9,17,25,..... must be taken to give a sum of 636​

Answer 1

given a= 9

d=17-9 =8

we know sum of AP=636

$\frac{n}{2} (2a + (n - 1)d) = 636$

$> \frac{n}{2} (2 \times 9 + (n - 1) \times 8) = 636 \\ > 9n + 4 {n}^{2} - 4n = 636 \\ > 4{n}^{2} + (53 - 48)n - 636 = 0$

>4n(n-12) + 53(n-12)=0

>(4n+53)(n-12)=0

>n=12

or

n=(-53/4)

Mark as brainlist please