Question

Verify that the differential coefficient with respect to \(x\) of \[\begin{equation*} \sin^4 x + 2 \cos^2 x - \cos^4 x \end{equation*}\]

is equal to \(0\) for all values of \(x\). What deduction can be made from this result?

[By ‘the differential coefficient’, the question means ‘the derivative’.]