Inequality for trigonometric function

70 Views Asked by At

How to prove the following inequality:

$\sin{x}+x\cos{x}\le\sqrt{1+x^{2}}$ for all $x\in\mathbb{R}$.

It seems to be related the function $f(x)=x\sin{x}$ and M.V.T., but, I'm not sure about that.

1

There are 1 best solutions below

1
On BEST ANSWER

Use the Cauchy Schwarz inequality

$$(\sin(x)+x\cos(x))^2\le (1^2+x^2)(\sin^2(x)+\cos^2(x))$$