I was given this question to take home and practice but we have not been shown anything like this before and there in nothing in the text like this either. If anyone has any tips on how to start this question I would really appreciate it.

Two surfaces are said to intersect orthogonally at a point P if their

tangent planes are perpendicular at the point P. Show that the surfaces z = (x^2)y and

y = 1/4x^2 + 3/4 intersect orthogonally at (1; 1; 1).

Thanks