[tex]f(x)=2\cdot3^x+1\\
y=2\cdot3^x+1\\
2\cdot 3^x=y-1\\
3^x=\frac{y-1}{2}\\
x=\log_3\frac{y-1}{2}\\
f^{-1}(x)=\log_3\frac{x-1}{2}\\
[/tex]
[tex]\alpha_{\text{rad}}=\alpha_{\text{deg}}\cdot\frac{\pi}{180}\\
\alpha_{\text{rad}}=1600\cdot\frac{\pi}{180}\\
\alpha_{\text{rad}}=\frac{80}{9}\pi\approx27.9
[/tex]
