a)Ta có `\hat{xOy} +\hat{yOz} = 150°`
`\hat{xOy}-\hat{yOz} = 90°`
`=> hat{xOy} +\hat{yOz} +\hat{xOy}-\hat{yOz} = 150° + 90° =240°`
`<=> 2\hat{xOy} = 240°`
`<=> \hat{xOy} =\frac{240}{2}=120°`
`=> \hat{yOz}=\hat{xOy} -90°= 120° -90° = 30° `
b) Trong hình