4. Show that the equation of the normal line to f(x, y, z) = c at (xo, yo, Zo) is given by the equation x = xo + fx(To, yo, zo)t, y = yo + fy(Xo, yo, zo) t, z = zo + fz(X0, yo, Zo) t, 5. Show that the equation of the tangent plane to f(x, y, z) = c at (x0, yo, 20) is given by the equation fx (Xo, yo, Zo) (x - x0) + fy(To, yo, Zo) (y - yo) + f= (XO, yo, Zo) (z - Zo) = 0