Question

Calcule a soma dos primeiros 20 termos da P.A (-10,-7,-4,..)

Answer 1

(-10,-7,-4,...)
r= -7-(-10)
r=-7+10 =3

a20=-10 +(20-1).3
a20=-10 +19.3
a20=-10+57
a20=47

S20= (-10+47).20/2
S20=(37).20/2
S20=740/2
S20= 370