Question 59941
<1 and <2 are supplementary since they are adjacent.  so <1+<2=180
<2 and <3 are supplementary for the same reason.   so <2+<3=180
solve for <1:   <1 = 180 - <2
solve for <3:   <3 = 180 - <2
<1 and <3 are equal to the same thing, so <1 = <3