`a)sinx=1/2`

`<=>sinx=sin(pi/6)`

`<=>x=pi/6+k2pi` hoặc `x=pi-pi/6+k2pi=(5pi)/6+k2pi(k\inZ)`

Vậy: `...`

`b)cosx=\sqrt{2}/2`

`<=>cosx=cos(pi/4)` 

`<=>x=pi/4+k2pi` hoặc `x=-pi/4+k2pi(k\inZ)`

Vậy: `...`

`c)sin2x=\sqrt{3}/2`

`<=>sin2x=sin(pi/3)` 

`<=>2x=pi/3+k2pi` hoặc `2x=pi-pi/3+k2pi=(2pi)/3+k2pi(k\inZ)`

`<=>x=pi/6+kpi` hoặc `x=pi/3+kpi(k\inZ)`

Vậy: `...` 

`d)2cos3x+1=0`

`<=>cos3x=-1/2`

`<=>cos3x=cos((2pi)/3)`

`<=>3x=(2pi)/3+k2pi` hoặc `3x=-(2pi)/3+k2pi(k\inZ)`

`<=>x=(2pi)/9+(k2pi)/3` hoặc `x=(-2pi)/9+(k2pi)/3(k\inZ)`

Vậy: `...`

`e)sin(x-pi/3)=1`

`<=>x-pi/3=pi/2+k2pi(k\inZ)`

`<=>x=pi/2+pi/3+k2pi(k\inZ)`

`<=>x=(5pi)/6+k2pi(k\inZ)`

Vậy: `...`

`f)cos(x+30^o)=-1`

`<=>x+30^o=180^o+k360^o(k\inZ)`

`<=>x=180^o-30^o+k360^o(k\inZ)`

`<=>x=150^o+k360^o(k\inZ)`

Vậy: `...`

`g)cosx=0`

`<=>x=pi/2+kpi(k\inZ)`

Vậy: `..`

`h)sin(2x+pi/6)=0`

`<=>2x+pi/6=kpi(k\inZ)`

`<=>2x=-pi/6+kpi(k\inZ)`

`<=>x=-pi/12+(kpi)/2(k\inZ)`

Vậy: `...`

`i)sin^2x=1/2`

`TH1:sinx=\sqrt{2}/2`

`<=>sinx=sin(pi/4)`

`<=>x=pi/4+k2pi` hoặc `x=(3pi)/4+k2pi(k\inZ)`

`TH2:sinx=-\sqrt{2}/2`

`<=>sinx=sin(-pi/4)`

`<=>x=-pi/4+k2pi` hoặc `x=(5pi)/4+k2pi(k\inZ)`

Vậy: `...`

`k)cos^2 2x=1`

`TH1:cos2x=1`

`<=>2x=k2pi(k\inZ)`

`<=>x=kpi(k\inZ)`

`TH2:cos2x=-1`

`<=>2x=pi+k2pi(k\inZ)`

`<=>x=pi/2+kpi(k\inZ)`

Vậy: `...`