Question

What is the first term in a geometric sequence if the common ratio is −4 and the sum of the first four terms is −255?

Answer 1

Sn=A1(1-r^n)/(1-r)
Sum of a finite geometric series formula
We know the sum, number of terms and rate, so you plug those in.
-255=A1(1-(-4)^4))/(1-(-4)
-255=A1(1-256)/5
-255=A1(-255)/5
-1275=A1(-255)
5=A1

Hope this helped! Let me know if you have any questions.