Find the radius of convergence of the Taylor series with the center at the origin (\(x_0=0\)) for the following function
- \[ f(x)=\frac {\sqrt {x+3}}{x^2+3} \]
- \[ f(x)=\frac {1}{(\cos x+3)^2} \]
(\(x\) is a real variable; you do not need to find the series themselves).