Let r(t)=⟨t2,∣t∣⟩. Which statement about r′(0) is true?
a) r′(0)=⟨0,0⟩ because both one–sided limits equal zero.
b) r′(0) does not exist because the second component is not differentiable at t=0.
c) r′(0)=⟨0,1⟩ since the right–hand derivative of ∣t∣ is 1.
d) r′(0) does not exist because the first component has a cusp at t=0.