tìm tập xác định: y= $\frac{tan5x}{sin4x-cos3x}$

ĐKXĐ: `{(cos5x ne 0),(sin4x - cos3x ne 0):}`

Ta có: `cos5x ne 0`

`<=>` `5x ne pi/2 + kpi` `(k in ZZ)`

`<=>` `x = pi/10 + (kpi)/5` `(k in ZZ)`

Ta có: `sin4x - cos3x ne 0`

`<=>` `sin4x ne cos3x`

`<=>` `sin4x ne sin(pi/2-3x)`

`<=>` `{(4x ne pi/2-3x+k2pi \ (k in ZZ)),(4x ne pi-pi/2+3x + k2pi \ (k in ZZ)):}`

`<=>` `{(7x ne pi/2 +k2pi \ (k in ZZ)),(x ne pi/2 +k2pi \ (k in ZZ)):}`

`<=>` `{(x ne pi/14 + (k2pi)/7 \ (k in ZZ)),(x ne pi/2 + k2pi \ (k in ZZ)):}`

Vậy `D = RR \\ {pi/10+(kpi)/5,pi/14+(k2pi)/7 | k in ZZ}`