So I have to find the equation of the tangent line then use the second derivative to see if the graph lies above or below the tangent line

the function is

$\displaystyle f(x) = x \sin 2x$ with a given x value of $\displaystyle x = \pi/4$ and so $\displaystyle f'(x) = \sin 2x + 2x \cos 2x $ and $\displaystyle f"(x) = 4(\cos 2x - x \sin 2x)$

when I solve $\displaystyle f(\frac{\pi}{4}) = \frac{\pi}{4}$

so this would just mean $\displaystyle y=x$ or I could say $\displaystyle \frac{\pi}{4} - y = \frac{\pi}{4} - x$

correct?

And the graph lies below the tangent line because solving because $\displaystyle f"(x) < 0$ as shown $\displaystyle f"(\frac{\pi}{4}) = - \pi$