Practicing Success
The number of values of $x$ where the function $f(x)=\cos x+\cos (\sqrt{2} x)$ attains its maximum is |
0 1 2 Infinite |
1 |
We have, $f(x)=\cos x+\cos \sqrt{2} x$ $\Rightarrow f(x)=2 \cos \left(\frac{\sqrt{2}+1}{2}\right) x \cos \left(\frac{\sqrt{2}-1}{2}\right) x \leq 2$ Clearly, $f(x)=2$ only when $\cos \left(\frac{\sqrt{2}+1}{2}\right) x=1 \text { and } \cos \left(\frac{\sqrt{2}-1}{2}\right) x=1 \Rightarrow x=0$ Hence, there is only one value of x where f(x) attains its maximum. |