What is the sum from n=1 to infinity of (cos(9))^n ?

The sum from n=1 to infinity of (cos(9))^n is converges

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sum from n=1 to infinity of (cos(9))^n

n = 1 \sum \infty (cos (9))^{n}

converges

Solution steps

n = 1 \sum \infty (cos (9))^{n}

n = k \sum \infty (a_{n}) = n = 0 \sum \infty (a_{n}) - a_{0} - a_{1} - \dots a_{k - 1}

= n = 0 \sum \infty (cos (9))^{n} - (cos (9))^{0}

n = 0 \sum \infty (cos (9))^{n} =

converges

= converges - (cos (9))^{0}

= converges

What is the sum from n=1 to infinity of (cos(9))^n ?
The sum from n=1 to infinity of (cos(9))^n is converges