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anonymous
 one year ago
Quadrilateral EFGH is inscribed inside a circle as shown below. Write a proof showing that angles H and F are supplementary.
anonymous
 one year ago
Quadrilateral EFGH is inscribed inside a circle as shown below. Write a proof showing that angles H and F are supplementary.

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mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Do you need a twocolumn proof or just an outline of the proof?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0just outline should be fine

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Ok. Here's the idea for this proof. A full circle is an arc of measure 360 deg.

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0dw:1434114713677:dw

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Let's look at two arcs on the figure.

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0so would we have to figure they both have to equal 180 right?

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0dw:1434114801663:dw

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0No. We don't know how much either arc measures. We do know that the sum of their measures is 360. Also, if we make an arc 180, and the other one has to also be 180, then this proof would only work when the arcs are 180 deg. We want a proof that works for all inscribed quadrilaterals, no matter what any of their angle measures are.

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Because of the above, we call the measure of one arc x. Since the sum of the measures of the arc is the entire circle, the arcs add up to 360 degrees.

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0so if one arc is x, the other arc must be 360  x. Ok so far?

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0dw:1434114997252:dw

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0so we would do 360 minus x for both angles?

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0We are not dealing with angles yet. So far, we are only dealing with arc measures. The measure of arc EHG is x. The measure of arc EFG is 360  x. This is all we have so far. Do you follow this so far?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0oh yeah I get it now.

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Great. Now we start with the angles. What do you know about an inscribed angle and its corresponding arc? Look at the figure below. What is the m<A? dw:1434115295031:dw

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0the arc is two times the measure of the angle correct?

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Exactly. An inscribed angle is half the measure of its arc. (A central angle is the same measure as the arc, but we're not dealing with a central angle here.)

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0dw:1434115526244:dw

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Ok. Let's go back to our problem, and look at the inscribed angles of the two arcs we are dealing with.

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0I marked in the figure the two angles of the two arcs we are dealing with. dw:1434115587886:dw

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Let's look at angle EFG first. Its arc is arc EHG. Arc EHG measures x. What is the measure of angle EFG?

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Exactly. It is half of the arc.

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0dw:1434115776669:dw

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Now let's look at the other arc and its corresponding inscribed angle. Arc EFG measures 360  x. What is the measure of the inscribed angle EHG?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0that would be half of 360 x so 1/2(360x)

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Exactly. Let me write that down.

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0dw:1434116074608:dw

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0We are trying to prove that opposite angles are supplementary. Angles EFG and EHG are opposite angles, so let's add their measures.

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0dw:1434116159157:dw Ok?

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Now let's simplify the right side.

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0We can factor out 1/2 dw:1434116259666:dw

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Now we combine the x's in the parentheses. x  x = 0, so we get: dw:1434116311737:dw

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Finally we get: dw:1434116353183:dw

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0The definition of supplementary angles is: Two angles are supplementary if their measures add up top 180 degrees. We have just shown that the two opposite angles have measures that add up to 180 degrees, so the opposite angles are supplementary.
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