Two angles are complimentary if the sum of their measures is 90 degrees.
If the measure of one angle is x degrees, represent
the measure of the other angle as an expression of x.
Let's think about this for a second. Let's pretend that one of our angles
is 70 degrees. What would be the measure of the other angle if they
had to add to be 90? If you said 20, you are correct!
The thought behind how we got that 20 is, the total of 90 is given,
we have already used 70, so we would subtract 70 from 90 and that would
tell us what the complimentary angle would have to be.
So, using x, we can write an expression
that shows that we take the total of 90 and subtract the given angle of x:
90 - x
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