Find the 15th term in the sequence using one of your formulas. Show your steps

Question

Find the 15th term in the sequence using one of your formulas. Show your steps

5,-20,80,-320

Answer 1

5, -20, 80, -320, ... is a geometic sequence

a1 =5, r = -4 = common ratio

an = a1r^(n-1)

a2 = a1(-4)^(2-1) = 5(-4) = -20

a15 = 5(-4)^(14)

a15= 1,342,177,280 = about 1 1/3 billion = about 1.34 x 10^9 in scientific notation