Cosine beyond 90
| The same can be done with cosine as with sine. Because cos is the length of the adjacent side, as a fraction of the hypotenuse, on 2D coordinates, with the hypotenuse 1 unit long, the cosine is the length OB |
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Here OB is on the negative part of the x-axis, so cos127 = -0.6 to 1 decimal place. |
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Plotting all of the values to get the graph of Cosine gives
This is the same as the sine curve, but translated by -90º along the
x-axis.Again the symmetry of the graph can be used to find the second of the two solutions:
| Eg. cos
x
= 0.75 x = 41·4º (from the calculator) x = 360 - 41·4 (from the symmetry of the graph) x = 318·6º And this can be checked on the calculator by doing cos 318·6º
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