Trigonometric identities

What the problems look like

A few statements from this skill. Answers, hints and worked solutions live in the practice session.

1. Warm-up

   Use a sum identity to find the exact value of $\cos(120^{\circ})\cos(30^{\circ}) - \sin(120^{\circ})\sin(30^{\circ})$.

2. Warm-up

   Use a sum identity to find the exact value of $\cos(60^{\circ})\cos(60^{\circ}) - \sin(60^{\circ})\sin(60^{\circ})$.

3. Warm-up

   Use a sum identity to find the exact value of $\cos(90^{\circ})\cos(60^{\circ}) - \sin(90^{\circ})\sin(60^{\circ})$.

Problems shown under their original terms: Generated (template, solver-computed).