Question

calcule a soma dos vinte primeiros termos da pa (0,15;040;065;0,9....)

Answer 1

a1 = 0.15
a2 = 0.40
r = 0.40 - 0.15 = 0.25 ***

a20 = a1 + 19r = 0.15  + 19 ( 0.25) = 0.15 + 4,75 =4,9 ****
S20 = ( 0.15 + 4.9) * 10
S20 = 5.05 * 10 = 50.5 ***