if x-1, x+3 and x+12 are consecutive terms in a geometric sequence what is the ratio.

I was told you put t3 over t2, and also t2 over t1 and cross multiply, which gives you a quadratic, but when I do it my (a) value is 0 so it would be

5 +/-5 over 0

?

then you sub that into the original equation? how do you sub x into tn=ar^n-1

or sn=a(r^n-1over r-1)?

thanks.