For part a), notice that \(\displaystyle f(x)=f(x+2k)\) for all integers \(\displaystyle k\). Thus, if you can solve the equation for the interval \(\displaystyle \[0,2)\) so that \(\displaystyle f(x_0)=2\), then we have the general solution that \(\displaystyle f(x_0+2k)=2\) for all integers \(\displaystyle k\). Then \(\displaystyle x=x_0+2k\) is your general solution.