InequalityHardQuestion 200030
Question
The number of values of x in [0, 2π] satisfying sin x > cos x is:
- Ax in (π/4, 5π/4)Correct
- Bx in (0, π/4)
- Cx in (π/4, π)
- Dx in (3π/4, 2π)
Correct answer
x in (π/4, 5π/4)
Explanation
sin x > cos x → sin x − cos x > 0 → √2 sin(x − π/4) > 0 → sin(x − π/4) > 0. This holds when x − π/4 ∈ (0, π) i.e. x ∈ (π/4, 5π/4).