Question

Find the sum of the first on terms of
the following A.P. as asked for:
2,6, 10, 14
up to 20 terms.​

Answer 1

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

= 20/2 × [2x2+(20-1)x4]

= 10×(4+19×4)

= 10×(4+76)

= 10x80

= 800

:-)