Question

Ребят решите срочно пожалуйста

Answer 1

$b_{1} = -5, b_{n} = -2* \frac{1}{b_{n-1}}, n > 1\\b_{n} = b_{1}*q^{n-1}\\b_{3} = -2 * \frac{1}{b_{2}}\\b_{1} * q^{2} = -2 * \frac{1}{b_{1} * q}\\ b^{2}_{1}*q^{3} = -2\\q^{3} = -\frac{2}{25}, q =  \sqrt[3]{-\frac{2}{25}}\\b_{3} = b_{1} * q^{2} = -5 * \sqrt[3]({-\frac{2}{25})^{2}}$