# Mclaurin's series

I am given $y=f(x)=tan(2tan^{-1}x+\frac{\pi}{4})$ for [ltex]-0.4<=x<=0.4[/tex] and asked to expand this using mclaurin's series which gives $g(x)=1+4x+8x^2+20x^3+...$
I was then asked to find the range of values of $x$ for which the values of $g(x)$ differs from $f(x)$ by less than $0.5$