anonymous 4 years ago how would i find the missing term of the geometric series a1 = 4, an = 324, r = 3

1. campbell_st

well it looks like you need to find the number of terms n use $T_{n} = ar^{n-1}$ then $324 = 4 \times 3^{n -1}$ you need to solve for n divide both sides by 4 $\frac{324}{4} = 3^{n -1}$ or $81 = 3^{n -1}$ express 81 as a power of 3 $3^4 = 3^{n -1}$ equate the powers 4 = n - 1 I'll let you finish the question

2. anonymous

ok thanks