# How do you find a_4 if a_1=-7 and r=-3/4?

##### 1 Answer
Dec 22, 2014

From a1 to a4 is three steps, so you multiply by -3/4 three times

This is what we call an arithmetic series. Every next item is calculated by multiplying the one before by the multiplicant r.
so a1=-7 a2=-7 x-3/4 and so on
Or in short (three steps!) a1 x r^3 = (-7)*(-3/4)^3