Question

Find the sum of 13 terms of an AP- 6,0, 6, 12....​

Answer 1

Answer:

390

Step-by-step explanation:

a=-6

d=0-(-6)=6

S13=n/2[2a+(n-1)d]

S13=13/2[-12+12×6]

S13=13/2[60]

S13=13×30

S13=390

Answer 2

Answer:

Sn= n/2×[2a+(n-1)d]

S13=13/2×[2×-6+(13-1)6]

S13=13/2×[-12+12×6]

S13=13/2×(-12+72)

S13=13/2×60

S13=13×30

sum of 13 terms is 390