Question

if first term of a G.P. is 5, the sum of the first 3 terms is 31/5 find the common ratio.

Answer 1

\[5 + 5r + 5r^2 = \frac
{31}{5}\]A quadratic equation. Find the two solutions and see which one works.

Answer 2

yes got it thanks :)

Answer 3

i spose if you want a simple solution that would be fine ... :)

Answer 4

i was thinking of:

\[5\frac{1-r^3}{1-r}=\frac{31}{5}\]

Answer 5

honestly i didn't use the sum formula because i couldn't remember it myself :P

Answer 6

1-r^3 = (1-r)(1+r+r^2) so it reduces that same