Given that the fourth term is 64 and the sum to infinity is 625, what is the value of u1 and the value of r?
u1 * r^3 = 64
u1/(1-r) = 625
so, dividing,
r^3(1-r) = 64/625
Now find r, and with that, get u1
hint: 64/625 = 4^3/(5^3 * 5)
u1/(1-r) = 625
so, dividing,
r^3(1-r) = 64/625
Now find r, and with that, get u1
hint: 64/625 = 4^3/(5^3 * 5)