Question

Find the sum of the first 20 terms of the A.P. : 13, 8, 3, .....

Answer 1

Answer:

Here is your answer........

Answer 2

Answer:

Step-by-step explanation:

Sⁿ = n/2[2a+(n-1)d]

a=13

d=-5

n=20

S₂₀= 20/2[2×13+(20-1)-5]

    = 10 [26-95]

    =10×(-69)

    = -690