6.05 Geometric series

Find the sum of the first $5$5 terms of the geometric sequence defined by $u_1=-7.916$u1​=−7.916 and $r=-2.274$r=−2.274.

Give your answer correct to two decimal places.

The sum of $n$n terms in the geometric series $1+5+25+\text{. . . }$1+5+25+. . . is $1525878906$1525878906.

Solve for $n$n, the number of terms.

Consider the series $3+1+\frac{1}{3}$3+1+13​ ...