Giải phương trình sau:

sin4x - cos5x = 0

`sin 4x - cos 5x = 0`

`=>sin 4x - sin(pi/2 - 5x) = 0`

`=>2cos((- 2x + pi)/4) * sin((18x - pi)/4) = 0`

`Th_1`

`cos(- (2x + pi)/4) = 0`

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

`Th_2`

`sin((18x - pi)/4) = 0`

`=>x = pi/18 + 2k(pi)/9(k in ZZ)`

`@Sad2006`