9 Using a formula find the 10 term of the geometric sequence

9.) Using a formula, find the 10 term of the geometric sequence: 64, -32, 16 10. Using a formula, find the sum of the first 10 terms in the geometric sequence: 2, 4, 8, 16

Solution

S = 64 , -32 , 16

an = a1r^n-1

r = -1/2

a10 = 64(-1/2)^9 = -64/2^9 = -2^6/2^9 = -1/8

10) Sum of G.P = a(r^n -1)/(r-1)

n =10 ; r = 2

= 2(2^10 -1)/(2 -1)

= 2046