Question 1032785
<pre>
Suppose &#8736;A and &#8736;B are supplementary and congruent.

Then since they are supplementary,

m&#8736;A + m&#8736;B = 180°

And since they are congruent,

m&#8736;A = m&#8736;B

Substituting equals for equals in m&#8736;A + m&#8736;B = 180°

m&#8736;B + m&#8736;B = 180°

2m&#8736;B = 180°

Divings both sides by 2

m&#8736;B = 90°

So &#8736;B is a right angle

And since m&#8736;B = m&#8736;A

m&#8736;A = 90°

So &#8736;B is a right angle

So it's true that they are both right angles.

Edwin</pre>