If the graph of a twice-differentiable function is concave down on the open interval

MATHEMATICS · Single correct · A Level · Mathematics · Differentiation · Differentiation

Problem

If the graph of a twice-differentiable function

f

is concave down on the open interval

(1,6)

, which of the following statements must be true for every

x

(1,6)

? (a)

f'(x)<0

(b)

f''(x)<0

(c)

f''(x)=0

(d)

f''(x)>0