Question

Numa P.G, a1 = -12 e q = 2. calcule a soma dos 20 primeiro termos dessa P.G

Answer 1

$a_{1}=-12\\\\q=2\\\\n=20\\\\ S_{n}= \frac{ a_{1*(q^n-1)} }{q-1}\\\\ S_{20}= \frac{-12*( 2^{20}-1) }{2-1}\\\\ S_{20}= \frac{-12*(1048576-1)}{1}\\\\ S_{20}=-12*(1048575)\\\\ S_{20}=-12582900$