Hoy many pairs of parallel lines does a Square have
2 answers:
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Pythagorean theorem is 
and using that sin is opposite/hypotenuse, you can find the third side of the triangle.
now you know adjacent is 60, so cos=60/61
and using that sin is opposite/hypotenuse, you can find the third side of the triangle.
now you know adjacent is 60, so cos=60/61