Solve cos(3x−20∘)=−12\displaystyle \cos(3x-20^\circ)=-\frac12cos(3x−20∘)=−21 for 0∘≤x<180∘0^\circ\leq x<180^\circ0∘≤x<180∘.
42 exam-style questions on CCEA A Level Maths 1.4.6 Trigonometry. Each one has a worked solution and a mark scheme showing where the marks go.