2. A geometric series is defined by an = -2(-5)". Find the geometric series of the first five terms.
3. A geometric sequence is defined by an = S, with as = 9.
Part A: Find the first six terms of the geometric sequence.
Part B: Determine the series of the first six terms.
4. Find the sum of the geometric series of the first five terms that is defined by a, = 16 (0)".

Ariana starts with 100 milligrams of a radioactive substance. the amount of the substance decreases by 20% each week for a number of weeks, w. the expression 100(1−0.2)w finds the amount of radioactive substance remaining after w weeks. which statement about this expression is true? a) it is the difference between the initial amount and the percent decrease. b) it is the difference between the initial amount and the decay factor after w weeks. c) it is the initial amount raised to the decay factor after w weeks. d) it is the product of the initial amount and the decay factor after w weeks.