Confusion over unexpected Math.cos behavior in Javascript -

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this question has answer here:

the cosine of 90 degrees 0.

i understand javascript's math.cos takes radians, i've tried:

math.cos(90 * math.pi / 180)

why yield 6.123233995736766e-17 instead of 0?

6.123233995736766e-17 0. it's 0.00000000000000006123233995736766. kind of minor error normal when working ieee floating point numbers.

the solution never compare numbers exactly, compare if within range expect. eg.

var result = math.cos(90 * math.pi / 180); if ( math.abs( result - 0 ) < 1e-16 ) {     // test passed, result 0 }

the - 0 nothing, more - x how compare x. trying compare 0, used - 0, leave off , same result.


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