Question 220931
All you have to know here is the definition of "complement and supplement"
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The measure of the supplement of an angle is 3 times as great as the measure of the angle's complement. 
Find the measure of the angle.
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let x = "the angle"
supplement = 180-x
complement = 90-x
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The equation for what it says (the word "is" usually means =): 
180-x = 3(90-x)
180 - x = 270 - 3x
-x + 3x = 270 - 180
2x = 90
x = {{{90/2}}}
x = 45 degrees
You can check the solution in the original equation
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The difference between the measures of the angle and its complement is 14.
 Find the measure of the angle and its complement.
x - (90-x) = 14
x - 90 + x = 14
x + x = 14 + 90
2x = 104
x = 52 degrees
Check solution in original equation
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Find the measure of an angle if it is 12 less than twice the measure of its complement.
x = 2(90-x) - 12
x = 180 - 2x - 12
x + 2x = 180 - 12
3x = 168
x = {{{168/3}}}
x = 56 degrees
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If a point C is equidistant from points A and B, then point C is the midpoint of the segment that joins A and B. OK, I agree with that!