Can somebody explain with steps. Thank You

Section 7.3 7. Rewrite the expression in terms of the first power of cosine: cos4x 8. Use an appropriate Half-Angle Formula to find the exact value of cos 165 9. Use the Addition Formula (from section 7.2) to prove the Double-Angle Formula for Sine 10. Verify that cos 4x - cos 6x = 2 sin 5x sin x (Hint: Use a sum-to-product formula)