很简单啦
因为角BOC=1/3平角-1/3角AOC
=1/3(平角-aoc)
=1/3(180-(1/3直角+1/3BOC))
=1/3(180-30-1/3BOC)
=1/3(150-1/3BOC)
BOC=50-1/9BOC
10/9BOC=50
BOC=45
又因为角AOC=1/3直角+1/3角BOC
=1/3(90+(1/3平角-1/3AOC))
=1/3(150-1/3AOC)
=50-1/9AOC
10/9AOC =50
AOC=45
所以 角AOC+ 角BOC=45+45 =90
所以OA垂直于OB