Chapter 7.2, Problem 3PT

The first step to evaluate ∫ cos⁴ x dx is to rewrite the integral as

1. a) ${{\displaystyle \int \left(\frac{1+\cos 2x}{2}\right)}}^{2}dx$
2. b) ${\displaystyle \int {\text{cos}}^{\text{3}}x\cdot \cos xdx}$
3. c) ${\displaystyle \int (1-{\sin }^{4}x)dx}$
4. d) ${\displaystyle \int {\text{cos}}^{\text{2}}x(1-{\sin }^{2}x)dx}$