Skip to main contentSkip to solution

If the function f(x)=sin⁡x+cos⁡x,0≤x≤2πf(x)=\sin x+\cos x, 0 \le x \le 2\pi is increasing in the interval (α,β)∪(γ,δ)(\alpha,\beta) \cup (\gamma,\delta), then α+β+γ+δ\alpha+\beta+\gamma+\delta is equal to:

Solution

✅ Correct Option: 3

f′(x)=cos⁡x−sin⁡x=2cos⁡(x+π4)>0f'(x) = \cos x - \sin x = \sqrt2\cos\left(x+\dfrac{\pi}{4}\right) > 0.

On [0,2π][0,2\pi] this holds for x∈(0,π4)∪(5π4,2π)x \in \left(0,\dfrac{\pi}{4}\right)\cup\left(\dfrac{5\pi}{4},2\pi\right).

So the sum is 0+π4+5π4+2π=7π20+\dfrac{\pi}{4}+\dfrac{5\pi}{4}+2\pi = \dfrac{7\pi}{2}.

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question