Question

find the sum of first 15 terms of the following ap
i)11,6,1,-4,-9
ii) 7,12,17,22,27
​

Answer 1

Answer:

(1)360

Step-by-step explanation:

(1) a=11, d=-5, n=15

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

=15/2[2(11)+(15-1)-5

=15/2[22+14(-5)]

=15/2(22-70)

=15/2(48)

=15(24)

=360