Question

What ia cos 16°? Please help me

Answer 1

This is a terrible question. Send the publisher a nasty note.

First let's answer the question.

Cosine is adjacent over hypotenuse, so the cosine of the angle labeled 16 degrees is 24 (the adjacent side to 16 degrees) divided by 25 (the hypotenuse).

Answer: 24/25

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Now I'm going to complain about the question.  24/25 is of course 0.96 exactly, while

cos 16° ≈ 0.96126169593831886191649704855706487352569

They're not the same, and never think 24/25 is the cosine of 16 degrees.  It's approximately the cosine of 16 degrees; there's a big difference.

The cosine of 16 degrees is some awfully complicated algebraic number, a zero of some high degree polynomial with integer coefficients.  Worse yet, the angle whose cosine is 24/25 is almost certainly a transcendental number, not the zero of any such polynomial.

Trigonometry as practiced forces approximations to be employed.  Let's not sweep that under the rug in the questions, please.