Question

. If a=2, d=4, Sn=128, find n.​

Answer 1

Step-by-step explanation:

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

128=n/2*(2*2+(n-1) 4)

128=n/2*(4+4n-4)

128=n/2*(4n)

128=2n²

n²=128/2

n²=64

n=8

hope it will help uhh