Question 189691
Draw a pic to see what's happening


1. AOC+COB=180 ...................... Given (linear pairs add to 180)
2. AOD+DOC+COE+EOB=180 ..... Break up angles (the drawing helps)
3. DOC+DOC+COE+COE=180 ..... Substitute
4. 2*DOC+2*COE=180 ......... Combine terms 
5. 2(DOC+COE)=180 .......... Factor
6. DOC+COE=90 .............. Divide
7. DOE=90 .................. Add angles