Question

express cos5A in terms of cosA ​

Answer 1

Step-by-step explanation:

Use the compound angle formulae. Then the double and triple angle formulae.

cos(2a + 3a) = cos(2a)cos(3a) - sin(2a)sin(3a)

= (2cos^2(a) - 1)(4cos^3(a) -3cos(a)) -