Answer
$y=2 \sin (\dfrac{\pi}{2})x$
Work Step by Step
As we can see from the given picture that the point$(1,2)$ is maximum, so the amplitude is $A=2$.
Thus, the time period $P$ will be: $P=4$
or, $\dfrac{2\pi}{k}=4$
This gives : $k=\dfrac{\pi}{2}$
But there is no horizontal shift, this means that $B=0$
Hence, our function is: $y=2 \sin (\dfrac{\pi}{2})x$
