Question

The sum of first 15 terms of the A.P. -10, -12, -14, -16, … is ………​

Answer 1

Answer:

The correct answer is -360.

Step-by-step explanation:

Let the first term and the common difference of the AP be a and d respectively.

Given,

a= -10

d= -12-(-10)

= -2

We know that,

Sn = n/2 {2a+(n-1)d}

•°• S15= 15/2 {2(-10)+(15-1)(-2)}

= 15/2 {-20+14(-2)}

= 15/2 (-20-28)

= 15/2*(-48)

= 15*(-24)

= -360

•°• Sum of the first 15 terms of the given AP is -360