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15. [-/1 Points] DETAILS Determine whether each statement is true or false. You have one submission for each statement. (a) f(x) is concave up on the interval (a,b) if f"(x) > 0 on (a,b). OTrue OFalse (b) f(x) is concave up on the interval (a,b) if f'(x) is increasing on (a,b). OTrue OFalse (c) f(x) has an inflection point at x = c if x = c is in the domain of f(x) and f"(c) = 0. True OFalse (d) f(x) has a relative minimum at x = c if f"(c) > 0. True False