Question

Write sin 81 degrees in terms of cosine

Answer 1

Answer:

Sine, cosine and tangent formulas are used in RIGHT triangles. So you have one 90 degree angle and two acute angles that add up to 90 degrees (they are complimentary). So the cosine of one angle would be the same as the sine of the compliment to that angle... and vice versa. To answer this question, sin 81 = cos 9, since 81 and 9 are the two acute angles of the triangle and they both add up to 90 degrees. "Cos 9" is the answer when you wish to write "sin 81" in terms of "cosine."

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