Skip to main contentSkip to solution

Consider a function f:[0,π2]→Rf:\left[0,\frac{\pi}{2}\right] \to R, given by f(x)=sin⁡xf(x)=\sin x and g:[0,π2]→Rg:\left[0,\frac{\pi}{2}\right] \to R, given by g(x)=cos⁡xg(x)=\cos x, Where R is a set of real numbers, Which of the following statements are correct?

(A) f and g are one-one

(B) f and g are not one-one

(C) f+g is not one-one

(D) f+g is one-one

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 1

On [0,π2][0,\frac{\pi}{2}], sin⁡x\sin x is strictly increasing and cos⁡x\cos x is strictly decreasing, so both are one-one and (A) holds.

(f+g)(x)=2sin⁡(x+π4)(f+g)(x)=\sqrt2\sin\left(x+\frac{\pi}{4}\right) peaks at x=π4x=\frac{\pi}{4}; for instance (f+g)(0)=(f+g)(π2)=1(f+g)(0)=(f+g)\left(\frac{\pi}{2}\right)=1, so it is not one-one and (C) holds.

Keyboard Shortcuts

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