Đáp án+Giải thích các bước giải:

 `sin(3x+20^{o})=cos(2x-20^{o})`

`sin(3x+20^{o})=sin(90^{o}-(2x-20^{o}))`

`sin(3x+20^{o})=sin(110^{o}-2x)`

`+)TH1: 3x+20^{o}=110^{o}-2x+k360^{o}`

`3x+2x=90^{o}+k360^{o}`

`5x=90^{o}+k360^{o}`

`x=18^{o}+72k\pi(k\inZZ)`

`+)TH2: 3x+20^{o}=180^{o}-(110^{o}-2x)+k360^{o}`

`3x+20^{o}=70^{o}+2x+k360^{o}`

`3x-2x=50^{o}+k360^{o}`

`x=50^{o}+k360^{o}(kinZZ)`

Vậy `S={18^{o}+k72^{o};50^{o}+k360^{o}|kinZZ}.`