`a)`
Ta có :
+ `cos alpha =sqrt3/2`
`=>hat alpha = 30^@`
+ `hat alpha + hat beta =90^@` ( `2` góc phụ nhau )`
`=>hat beta = 90^@ - hat alpha`
`=90^@ - 30^@`
`=60^@`
`b)`
Ta có :
+ `cos beta =2/5`
`=>hat beta ≈ 66^@`
+ `hat alpha + hat beta =90^@` ( `2` góc phụ nhau )`
`=>hat alpha= 90^@ - hat beta`
`=90^@ - 66^@`
`=24^@`
`c)`
Ta có :
+ `tan alpha =2`
`=>hat alpha ≈ 63^@`
+ `hat alpha + hat beta =90^@` ( `2` góc phụ nhau )`
`=>hat beta = 90^@ - hat alpha`
`=90^@ - 63^@`
`=27^@`