$2.$ Consider the surface z $=$ x$2+$y$21.($a$)$ Find the equation of the tangent plan to this surface at $(100).$ What is a unit normal vector to the surface here? $[$Hint: This surface can be expressed as a level surface for the function F$($xyz$)=$ x$2+$y$2$z $=1.$ What do you know about gradient vectors of level surfaces?$]($b$)$ Viewing the surface z $=$ x$2+$ y$21$ as a level set of a function F$($x$,$y$,$z$)$ and using the gradient, nd all points $($x$0$ y$0$ z$0)$ on this surface where the normal vector to the surface is parallel to the line through the point $($x$0$ y$0$ z$0)$ and the origin