Bài 5:
a) Ta có:
`hat{AOC} < hat{AOB}`
`=> OC` nằm giữa `OB` và `OA`
b) Ta có:
`hat{BOC} + hat{COA} = hat{AOB}`
`=> hat{BOC} = hat{AOB} - hat{COA} = 85^0 - 30^0 = 55^0`
c) Ta có:
`hat{BOD} + hat{BOA} = 180^0`
`=> hat{BOD} = 180^0 - hat{BOA} = 180^0 - 85^0 = 95^0`
Bài 7:
`a)` Ta có:
`hat{tOx} = 1/4.hat{xOy} = 1/4.60^0 = 15^0`
`=> hat{yOt} = 60^0 - hat{tOx} = 60^0 - 15^0 = 45^0`
`b)` Ta có:
`hat{tOy} - hat{tOx} = 10^0`
`=> hat{tOy} = 10^0 + hat{tOx}`
Mà: `hat{tOy} + hat{tOx} = hat{xOy} = 60^0`
`=> hat{tOx) + 10^0 + hat{tOx} = 60^0`
`<=> 2.hat{tOx} = 50^0`
`<=> hat{tOx} = 25^0`
`=> hat{tOy} = 10^0 + 25^0 = 35^0`
