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Editorial Team
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Asked: 2026-06-16T22:57:10+00:00

Shouldn’t the following statement hold? assertTrue(Double.isNaN(Math.tan(Math.acos(0d)))); But instead of Double.NaN Java returns 6.123233995736766 *

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Shouldn’t the following statement hold?

assertTrue(Double.isNaN(Math.tan(Math.acos(0d))));

But instead of Double.NaN Java returns

6.123233995736766 * 10^-17

on my 64-bit box.

EDIT:
This was a Copy and Paste error. In fact Java returns 1.633123935319537E16

I’m aware that this is because of the floating point representation, but i was under the impression that those undefined values of the tangent function would get the same treatment as e.g. Math.sqrt(-1d) but I guess in this case java.lang.Math just checks if the argument is positive before evaluating.

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1 Answer

  1. Editorial Team

    I get something different.

    System.out.println(Math.tan(Math.acos(0d)));
// and the tan for the next representable value.
System.out.println(Math.tan(Math.acos(0d) + Math.ulp(Math.acos(0d))));

    prints

    1.633123935319537E16
-6.218431163823738E15

    A 64-bit floating point cannot represent PI/2 exactly (it has an infinite number of digits) it represents a number close to this value and the tan() of this value is finite.

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