14: The chart for monotonicity is

There are adjoint intervals of the same monotonicity. To see whether we can connect there we need to investigate what happens at the connecting point. Going there from the left, the function is first decreasing and goes to f ((−1)^-) = 0, then it jumps up to f (−1) = f ((−1)⁺) = π/4 > 0 and then it goes down again, so we cannot connect the two intervals into one.

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