Let f be twice-differentiable on (1,3) with f′′(x)>0 for all x in that interval. The tangent line to f at x=2 is used to approximate f(2.1). Which of the following describes the relationship between the approximation T and the actual value f(2.1)?
a) The information given is insufficient to determine whether T overestimates or underestimates f(2.1).
b) T is an overestimate because f′′(2)>0 implies the slope is increasing, placing the tangent line above the curve to the right of x=2.
c) T is an underestimate because the graph of f is concave up on (1,3).
d) T is an overestimate because the graph of f is concave up on (1,3).