Hi. I suspect the downvote is from you. All I can say is that an incomplete question deserves an incomplete answer. Anyway, my answer is actually sufficient to enlighten your enquiry.

However I will still throw you a lifeline. The derivative of a curve is commonly known as the gradient of the curve. I assume your question showed/told you that your f'(x) curve concaves downwards. This means that the derivative of f'(x) [namely f"(x)] is negative.