Trigonometry Tricks

cos(90° - x) = sin x

sin(90° - x) = cos x


cos 75° = .259...

cos 15° = .259...

cos 45° = .707...

sin 45° = .707...

(Notice that the sine & cosine of 45 degrees are exactly the same!)

By the way, the cosine & sine of 45 degrees are equal to the square root of 1/2!

I almost forgot that most of the time, sines, cosines, tangents and such are irrational numbers; this explains the triple periods after the numbers in the examples.

Something to remember about real numbers:

Any number you can't get by dividing 2 integers is called irrational.

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© Derek Cumberbatch