(a)[5]
For $k = 3$, determine the exact solutions of $f(x) = 0$.
(b)[5]
Use the quadratic formula to demonstrate that, when $k > 5$, the equation $f(x) = 0$ has no solutions.
Mathematics 9709 · AS & A Level · Quadratics
Quadratics — practice question
The function $f$ is defined by $f(x) = 4\cos^4 x + \cos^2 x - k$ for $0 \leq x \leq 2\pi$, where $k$ is a constant.