3. Given $A(-1,2)$ is a point on the parabola $y=2 x^{2}$, line $l$ passes through point $A$ and is tangent to the parabola, then the equation of line $l$ is $\qquad$
3. $4 x+y+2=0$ From $y=2 x^{2}, y^{\prime}=4 x,\left.y^{\prime}\right|_{x=-1}=-4$, thus the equation of $l$ is $y-2=-4(x+1)$.