9. Which of the following equations have real solutions? (1) $x^{3} + x - 1 = 0$ (2) $2^{x} + 2^{-x} = 0$ (3) $\log_{2} x + \log_{x} 2 = 1$ (4) $\sin x + \cos 2x = 3$ (5) $4 \sin x + 3 \cos x = \frac{9}{2}$
& 1，5 & \multirow{2}{*}{D} & 21 & 1 & & 31 & 1
9. Which of the following equations have real solutions?\\
(1) $x^{3} + x - 1 = 0$\\
(2) $2^{x} + 2^{-x} = 0$\\
(3) $\log_{2} x + \log_{x} 2 = 1$\\
(4) $\sin x + \cos 2x = 3$\\
(5) $4 \sin x + 3 \cos x = \frac{9}{2}$