1) If given a surface with the equation z=x^2+ y^2 and we need to find the parametric equation of line perpendicular to the tangent plane at the point (a, b, a^2+b^2). We can find the del (x,y,z) and then substitute the point to the del and finally we write it into the parametric form of line(a+t(b)) ? 2) If ABCD is a square, M and N be the midpoint of AB and BC respectively. Lines AN and DM intersect at P, lines AN and CM intersect at Q, lines CM and DN intersect at R. how we are going to show that the [area AMP+ area BMQN + area of CNR ]=area DPQR if we using vector method? Using the properties of addition and subtraction of vector?