Question

calcule a soma dos 100 termos da PA (1000, 995,..)

Answer 1

an=a1+(n-1).r
a100= 1000+(100-1).(-5)
a100= 1000+ 99.(-5)
a100= 1000 -495
a100= 505

Sn= (a1+an).n/2
S100=(1000+505).100/2
S100= 1505.100/2
S100= 150500/2
S100= 75250