Question

Dado a PA (-2,-4...)Determine a soma dos 6 primeiros termos.

Answer 1

r=a2-a1=(-4)-(-2)=-4+2=-2
a6=a1+5*r=-2+5*(-2)=-12
S6=$r=a_{2}-a_{1}=(-4)-(-2)=-4+2=-2 \\ a_{6}=a_{1}+5*r=-2+5*(-2)=-12 \\ S_{6}= \frac{(a_{1}+a_{6})*6}{2} \\ S_{6}= \frac{(-2-12)*6}{2} \\ S_{6}=-42$