Question

Calcule a razão de uma P.A, sabendo que a2= -11 . a12= 19

Answer 1

an=a1+(n-1)r
a2=a1+(2-1)r
a2=a1+r

a12=a1+(12-1)r
a12=a1+11r

a2=a1+r
a2=-11
a1+r=-11
a1=-11-r

a12=a1+11r
a12=19
a1+11r=19
-11-r+11r=19
10r=19+11
10r=30
r=30/10
r=3