A fly is standing on a boulder, which is rolling down a hill. The forward torque the fly exerts on the boulder when it has rolled $x$ meters, in newton meters, is given by $\qquad \tau(x) = \dfrac{2}{1000}\sin\left(\dfrac{2\pi (x+0.2)}{4}\right)$. **What is the midline of this function? Give an exact answer.** $y = $ [[☃ math-keypad 1]]