# Dig the Range

Geometry Level 5

$\large \displaystyle f(x)=\left(\cos^{-1}\dfrac{x}{2}\right)^2+\pi \sin^{-1}\dfrac{x}{2}-\left(\sin^{-1}\dfrac{x}{2}\right)^2+\dfrac{\pi^2}{12}(x^2+6 x+8)$

If the range of $f(x)$ above is $[a\pi^2,b \pi^2]$, what is the value of $2(a+b)$?

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