Answer
$2\sin x$
Work Step by Step
Given that graph is of trigonometric function and starts with 0
Using general equation $y = k + A\sin (Bx + C)$
$Amplitude = |A|$
$Period = \frac{2\pi}{B}$
$Horizontal\ shift = –\frac{C}{B}$
$Vertical\ shift = k$
Period is $2\pi$ this gives B = 1
Amplitude is 2 so $A=2$
No vertical shift found as average of maximum and minimum is 0
so k = 0
The graph has
y = 0 at $x = 0, 2\pi => C = 0$
y = 2, at x = $\frac{\pi}{2}$
y = -2, at $x = \frac{3\pi}{2}$
Putting all these information together
we deduce that graph is of $2\sin x$