13. Look for a pattern!!

1/2 + 1/2²= 3/4 1/2 + 1/2² + 1/2³ = 7/8 1/2 + 1/2² 1/2³ + 1/2⁴ = 15/16

a) What is: 1/2 + 1/2² + 1/2³ + 1/2⁴ + 1/2⁵ + 1/2⁶ + 1/2⁷ + 1/2⁸ = ???

b) What is the pattern?