tìm txđ của các hàm số sau :

`a)`

ĐKXĐ: `sin(4x-pi/6) ne 0`

`<=>` `4x-pi/6 ne kpi` `(k in ZZ)`

`<=>` `4x ne pi/6 + kpi` `(k in ZZ)`

`<=>` `x ne pi/24 + (kpi)/4` `(k in ZZ)`

`=>` `D = RR \\ {pi/24 + (kpi)/4, k in ZZ}`

`b)`

ĐXKĐ: `cos(2x+pi/4) ne 0`

`<=>` `2x+pi/4 ne pi/2 + kpi` `(k in ZZ)`

`<=>` `2x ne pi/4 + kpi` `(k in ZZ)`

`<=>` `x ne pi/8 + (kpi)/2` `(k in ZZ)`

`=>` `D = RR \\ {pi/8 + (kpi)/2, k in ZZ}`

`c)`

ĐKXĐ: `cos(3x+pi) ne 0`

`<=>` `3x+pi ne pi/2 + kpi` `(k in ZZ)`

`<=>` `3x ne -pi/2 + kpi` `(k in ZZ)`

`<=>` `x ne -pi/6 + (kpi)/3` `(k in ZZ)`

`<=>` `x ne pi/6 + (kpi)/3` `(k in ZZ)`

`=>` `D = RR \\ {pi/6 + (kpi)/3, k in ZZ}`

`d)`

ĐKXĐ: `{(sin2x ne 0),(cot2x + 1 ne 0):}`

`<=>` `{(2x ne kpi \ (k in ZZ)),(cot2x ne -1):}`

`<=>` `{(x ne (kpi)/2 \ (k in ZZ)),(2x ne (3pi)/4 + kpi \ (k in ZZ)):}`

`<=>` `{(x ne (kpi)/2 \ (k in ZZ)),(x ne (3pi)/8 + (kpi)/2 \ (k in ZZ)):}`

`=>` `D = RR \\ {(kpi)/2,(3pi)/8+(kpi)/2, k in ZZ}`