Question

find the sum of 76 terms of A.P ,-5+(-8)+(-11)+.......+(-230)​

Answer 1

So, a= -5, d= -8-(-5)=-3,

First calculate the number in series.....

l=a+(n-1)d

-230=-5+(n-1)-3

-225=-3n + 3

3n=228

n=76.

Now,

Sum of the series  = n/2 (a+l)

 76/2 (-5-230)

38 * -235  = -8930.

So, the sum of your series would be -8930.