Suppose you need to know an equation of the tangent plane to a surface s at the point p (2,1,3). you don't have an equation for s but you know that the curves:
r1(t) = (2+3t, 1-t^2, 3-4t+t^2)
r2(t) = (1-u^2, 2u^3-1, 2u+1)
both lie on s. find an equation of the tangent plane at p.
*note: both r1 and r2 are vectors