Question

calcule a soma dos 20 primeiros termos da P.A (0,15; 0,40; 0,65; 0,9;...)

Answer 1

............................................................ nessa conta vai dar 25

espero que esteja certo

Answer 2

r=a2-a1
r=0,40-0,15=0,25

$an=a1+(n-1)r$
$a20=a1+(20-1)r$
$a20=a1+19r$
$a20=0,15+19.0,25$
$a20=0,15+4,75$
$a20=4,9$
-------------------------------------------------------------------------------------------------------
$Sn= \frac{n(a1+an)}{2}$
$S20= \frac{20(a1+a20)}{2}$
$S20= \frac{20(0,15+4,9)}{2}$
$S20= \frac{20.5,05}{2}$
$S20= \frac{101}{2}$
$S20= 50,2$