m∠b = 180° - x
That is the expression that represents the number of degrees of angle b.
Two angles A and B are supplementary only if their measures add up to 180 degrees.
Then we can write the simple equation:
m∠A + m∠B = 180°
In this case, we know that we have two angles a and b that are supplementary, and the measure of angle a is equal to x, where x is a variable, then using the above equation we can write:
m∠a + m∠b = 180°
Replacing the measure of angle a by the variable we get:
x + m∠b = 180°
Solving this for the measure of angle b we get:
m∠b = 180° - x
That is the expression that represents the number of degrees of angle b.
If you want to learn more about supplementary angles:
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