Infinite series

1003108806

Level: 
B
We are given the equation \[ \sum\limits_{n=1}^{\infty}(x+2)^{2n} =\frac13 \] with the unknown \( x \) being a real number. What is the set of all its solutions?
\( \left\{ -\frac32;-\frac52 \right\} \)
\( \left\{ -\frac32\right\} \)
\( \left\{ -\frac52 \right\} \)
\( \left\{\ \right\} \)
\( \left\{ \frac32;\frac52 \right\} \)

1003108809

Level: 
B
We are given the equation \[ \sum\limits_{n=1}^{\infty} (\sin x)^{2n-2}=2\cdot\,\mathrm{tg}\,x \] with the unknown \( x \) being a real number. What is the set of all its solutions?
\( \bigcup\limits_{k\in\mathbb{Z}}\left\{\frac14\pi+k\cdot\pi\right\} \)
\( \bigcup\limits_{k\in\mathbb{Z}}\left\{\frac34\pi+k\cdot\pi\right\} \)
\( \bigcup\limits_{k\in\mathbb{Z}}\left\{\frac34\pi+k\cdot\frac{\pi}2\right\} \)
\( \bigcup\limits_{k\in\mathbb{Z}}\left\{\frac18\pi+k\cdot\frac{\pi}2\right\} \)
\( \bigcup\limits_{k\in\mathbb{Z}}\left\{\frac14\pi+k\cdot\frac{\pi}2\right\} \)