A curve is defined parametrically by x=t2+1 and y=t3−3t, where t∈R.
a. (i) Determine all real values of t at which the tangent to the curve is horizontal.
b. (ii) Determine all real values of t at which the tangent to the curve is vertical.
c. (iii) List the Cartesian points corresponding to all the t obtained in parts (i) and (ii). State whether the curve possesses any point where the tangent could be both horizontal and vertical, giving a brief reason for your answer.