Question

What is the sum of the first seven terms of the geometric series where a1 = 10 and r = −2?

Answer 1

$Sum_{7} = 10 * \frac{1- (-2^{7}) }{1 - (-2)} = 10* \frac{1+128}{1+2} = 10* \frac{129}{3} = 10 * 43 = 430$