Question

If $x$ is positive, the values of $f\left(x\right)=-3\cos \sqrt{3+x+x^2}$ lies in the interval

• A. $[-1,3]$
• B. $[-3,3]$
• C. $[0,3]$
• D. $[-3,0]$

Answer 1

The correct option is B $[-3,3]$

$f\left(x\right)=-3\cos \sqrt{3+x+x^2}$
Since $-1⩽\cos \theta ⩽1$
So $-3⩽f\left(x\right)⩽3$