Solve cos t cos(2t) + sin t sin(2t) = sqrt(3)/2 on the interval from 0 to 2 pi.

1. The left side matches cos a cos b + sin a sin b, which is the difference formula for cosine. 2. So it collapses to cos(t - 2t), that is cos(-t). 3. Cosine is even, so cos(-t) = cos t, and the equation becomes cos t = sqrt(3)/2. 4. The reference angle for that value is pi/6. 5. Cosine is positive in quadrants I and IV, so the solutions are pi/6 and 2 pi - pi/6 = 11 pi/6. 6. The pair pi/6 and 5 pi/6 would solve sin t = 1/2 instead, so it answers the wrong function. _Source: OpenStax Algebra and Trigonometry (CC BY 4.0), Ch 9 "Trigonometric Identities and Equations", section 9.5 Solving Trigonometric Equations_