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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sine 81 degrees in terms of cosine is cos 9°
sin 81°
The angle is less than 90 degrees.it is an acute angle. Therefore, its in the first quadrant. The first quadrant, sine, cosine and tangent are positive.
sin 81° is less than 90 degree. Therefore, let's express them in terms of a cofunction.
Therefore,
sin x = cos(90 - x)
sin 81 = cos(90 - 81)
Therefore,
sin 81° = cos 9°
learn more on sine here: https://brainly.com/question/11962279
