Question

dada a sequencia (3,-3,3,-3,3,-3,...),calcule a S30.

Answer 1

Temos uma Pg de razão = -1

$\\ a_{1} =3 \\ \\ q = -1$

$\\ S_{n} = a_{1} *\frac{(q^n-1)}{q-1} \\ \\ S_{30} = 3* \frac{(-1)^3^0-1}{-1-1} \\ \\ S_{30} = 3* \frac{1-1}{-2} \\ \\ S_{30}= 3* \frac{0}{-2} \\ \\ S_{30} = 0$