Answer
$y=cos(x-\frac{\pi}{6})$
Work Step by Step
The graph appears to be the result of $y=cos(x)$ shifted $\frac{\pi}{2}-\frac{\pi}{3}=\frac{\pi}{6}$ units to the right, thus the function is $y=cos(x-\frac{\pi}{6})$
Note: if you use $y=sin(x)$, you will have $d\lt 0$
