Step 4 Now, let f"(x) = 0 and solve for x. Remember that f"(x) = - sin is a periodic function, and thus there are infinitely many angles that satisfy the condition. For this step, just give the three angles when 0 S x S 87. (Enter your answers as a comma-separated list.) 1 sin 16 = 0 4 sin * = 0 4 A = sin 1(0) + in (where n is an integer) X= Out of those three values, only x = is inside the open interval (0, 8Tr). We discard the others, because concavity cannot change at the terminal point of the domain of a function. Submit Skip (you cannot come back) eBook Submit