Question

quantos termos tem a p.a onde a1= 8, an= -30 e r= -2?

Answer 1

A PA tem 20 termos
a1=8 r=-2 an=-30 n=
an=a1+(n-1)r
-30=8+(n-1)(-2)
-30=8+(-2n+2)
-30=8-2n+2
-30-8-2=-2n
-40=-2n (-1)
2n=40
n=40/2
n=20