A geometric series has first term a and common ratio r where r\geqslant 1
The sum of the first four terms of this series is 15 times the first term.
a) show that r^3 + r^2 +r -14=0
and having S4 = 15a
I've done the first part
But I don't get b
b) Show that r=2 is the only real solution for this equation.
Every time I use Latex I get an error when I preview, has anything changed?