In triangle ABCABCABC, side AB AB\,AB has length k cmk\text{ cm}k cm, side BC BC\,BC has length 9 cm and side AC AC\,AC has length 7 cm.
Find the cosine of angle ACBACBACB, giving your answer as a fraction in its simplest form in terms of kkk.
Find the exact area of the triangle in terms of kkk.
217 exam-style questions on Edexcel A Level Maths Trigonometric Ratios, covering 9.1 The Cosine Rule, 9.2 The Sine Rule, 9.3 Areas of Triangles, 9.4 Solving Triangle Problems, 9.5 Graphs of Sine, Cosine and Tangent, and 9.6 Transforming Trigonometric Graphs. Each one has a worked solution and a mark scheme showing where the marks go.