The curve defined parametrically by x(t)=t2 and y(t)=t3 is considered at t=−1. Which statement best describes its concavity at that point?
a) The concavity cannot be determined because dtdx=0 at t=−1.
b) The curve is concave down because dx2d2y<0 at t=−1.
c) The curve is concave up because dx2d2y>0 at t=−1.
d) The point is an inflection point because dx2d2y=0 at t=−1.