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ANSWERS: 1
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pi radians = 180 degrees. in degrees: cos(45 - 180) = cos(-135) It helps to draw a graph of cos and sin at this point. Referring to the graph: cos(x) = sin(x+90) sin(x) = -sin(-x) so cos(-135) = -sin(45) Draw a right triangle with legs sqrt(2) and sqrt(2). The angle is 45. The hypotenuse is 2 by Pythagoras. sin(45) is sqrt(2)/2 by SOHCAHTOA. So cos(-135) = -sqrt(2)/2
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