Question

Evaluate f(x)=7cos2x f(-pi/4)

Answer 1

`f(x)=7\cos(2x)\hspace{5em}f\left( -(\pi )/(4) \right)=7\cos\left( -(\pi )/(4) \right) \\\\\\ f\left( -(\pi )/(4) \right)=7\left( (√(2))/(2) \right)\implies f\left( -(\pi )/(4) \right)=\cfrac{7√(2)}{2}`