Answer
$y=4\ sin(2x)$
Work Step by Step
Step 1. As the curve is odd and decreases while passing $(0,0)$, we can write a general form $y=A\ sin(kx)$
Step 2. We can identify the amplitude $A=4$.
Step 3. We can identify the period $p=\pi$, thus $\frac{2\pi}{k}=\pi$ and $k=2$
Step 4. The equation is $y=4\ sin(2x)$
