Find the reference angle of 100 degrees

Since the angle  

100 °  is in the second quadrant, the reference angle formula is  A r = 180 ° −

A c.   A r = 180 ° − 100 °

The reference angle is  A r = 80 ° .

80 °

in problems involving proportions, we can use cross products to test whether two ratios are equal and form a proportion. to find the cross products of a proportion, we multiply the outer terms, called the extremes, and the middle terms, called the means.

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