Question

Question 16
The sum of first 16 terms of the AP 10, 6, 2, … is

A) -320
B) 320
C) -352
D) -400​​​​​​​

Answer 1

Given AP is 10, 6, 2, ...
Here, the firstterm, a = 10.
Common difference, d = 6-10 = - 4
$\therefore S_{16}=\frac{16}{2}[2a+(16-1\left)d\right][\because S_n=\frac{n}{2}\{2a+(n-1)d\left\}\right]$
$=8[2\times 10+15(-4\left)\right]$
$=8(20-60)=8(-40)=-320$