Question

ME AJUDEMMM

PROGRESSAO ARITMETICA:

calcule a soma dos vinte primeiros termos  da PA(-45, -41,..)

Answer 1

$a_2_0 = a_1+19r\\\\ a_2_0 = -45+19*4\\\\ a_2_0 = -45+76\\\\ \boxed{a_2_0=31}$

$\boxed{S_n=\frac{(a_1+a_n)*n}{2}}\\\\ S_2_0 = \frac{(-45+31)*20}{2}\\\\ S_2_0 = -14*10\\\\ \boxed{S_2_0=-140}$