Why are the values for sine and cosine equal at 45°?

At 45° in a right triangle, the other acute angle is also 45°, so the two legs are equal. The side opposite the 45° angle therefore has the same length as the side adjacent to it. Since sine is opposite ÷ hypotenuse and cosine is adjacent ÷ hypotenuse, the two values are equal. This is choice D.

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