Question

Encontre a soma dos 15 primeiros termos da P.A(27,36,45,54,...)​

Answer 1

a1 = 27

r = 9

$an = 27 + (15 - 1) \times 9 \\ an = 27 + 126 \\ an = 153$

$s15 = \frac{(27 + 153) \times 15}{2} = \frac{2700}{2} \\ s15 = 1350$