5 The function f is such that \(\mathrm { f } ( x ) = 2 \sin ^ { 2 } x - 3 \cos ^ { 2 } x\) for \(0 \leqslant x \leqslant \pi\).
- Express \(\mathrm { f } ( x )\) in the form \(a + b \cos ^ { 2 } x\), stating the values of \(a\) and \(b\).
- State the greatest and least values of \(\mathrm { f } ( x )\).
- Solve the equation \(\mathrm { f } ( x ) + 1 = 0\).