Consider the following: x = t ln t, y = t ? ln t. Find dy/dx and d²y/dx². For which values of t is the curve concave upward? (Enter your answer using interval notation.)
a) dy/dx = 1/t, d²y/dx² = -1/t², concave upward for t > e
b) dy/dx = ln(t) + 1, d²y/dx² = 1/t, concave upward for t > e
c) dy/dx = t + ln(t), d²y/dx² = 1 + 1/t, concave upward for t < e
d) dy/dx = t + ln(t), d²y/dx² = 1 - 1/t, concave upward for t > e