Question

2. The sum of the third and the seventh terms

of an AP is 6 and their product is 8. Find
the sum of first sixteen terms of the AP.​

Answer 1

Explanation:

a3+a7=6

a+2d+a+6d=6

2a+8d=6

a+4d=3..... (1)

a+2d)(a+6d)=8

(3-4d+2d)(3-4d+6d)=8

(3-2d)(3+2d)=8

9-4d^2=8

d=1/2

a=1

s16=n/2 [2a+(n-1) d]

=8 (2+15/2)

=8×19/2

=76