(B)(B) When f ′ is positive, f increases. By the Fundamental Theorem of
Calculus, f ′(x) = 1 − 2 (cos x)^3 . Graph f ′in [0, 2π] × [−2, 4]. It is clear
that f ′ > 0 on the interval a < x < b. Using the calculator to solve 1 −
2(cos x)^3 = 0 yields a = 0.654 and b = 5.629.(C)