để kiểm tra 1 tiết toán của bọn tớ đây, bạn có thể tham khảo
câu1, [TEX]cosx- \sqrt{3}sin x = \sqrt{2}[/TEX]
[TEX]\Leftrightarrow \frac{1}{2}cosx-\frac{\sqrt[3}}{2}sinx=\frac{\sqrt{2}}{2}[/TEX]
[TEX]\Leftrightarrow cos(\frac{\pi}{3}-x)=cos\frac{\pi}{4}[/TEX]
.....
câu 2, [TEX]sinx +sin3x +sin5x=0[/TEX]
[TEX]\Leftrightarrow 2sin3xcos2x+sin3x=0[/TEX]
[TEX]\Leftrightarrow sin3x(2cos2x+1)=0[/TEX]
....
câu 3,[TEX]cos2x - tan^2x =\frac{cos^2x +cos^3x -1}{cos^2x}[/TEX]
Đk..
PT [TEX]\Leftrightarrow cos2xcos^2x-\frac{sin^2x}{cos^2x}.cos^2x=cos^2x+cos^3x-1[/TEX]
[TEX]\Leftrightarrow cos2xcos^2x-sin^2x-cos^2x-cos^3x+1=0 [/TEX]
[TEX]\Leftrightarrow cos2xcos^2x-cos^2x+cos^2x-cos^3x=0[/TEX]
[TEX]\Leftrightarrow cos^2x(cos2x-cosx)=0[/TEX]
.....
cấu 4:[TEX] cos2x +2sinx -1 -2sinxcos2x =0[/TEX]
[TEX]\Leftrightarrow (cos2x-1)-2sinx(cos2x-1)=0[/TEX]
[TEX]\Leftrightarrow (cos2x-1)(1-2sinx)=0[/TEX]
....
câu 5: [TEX] cosx +cos3x =1 +\sqrt{2}sin(2x+\frac{\pi}{4})[/TEX]
[TEX]\Leftrightarrow cosx+cos3x=1+sin2x+cos2x[/TEX]
[TEX]\Leftrightarrow cosx+cos3x=1+sin2x+(2cos^2x-1)[/TEX]
[TEX]\Leftrightarrow 2cos2xcosx=2sinxcosx+2cos^2x[/TEX]
[TEX]\Leftrightarrow 2cosx(cos2x-sinx-cosx)=0[/TEX]
....
câu 6:[TEX]\frac{sin^4(2x) +cos^4(2x)}{ tan(\frac{\pi}{4} -x).tan(\frac{\pi}{4}+x)} = cos^4(4x)[/TEX]
Ta có [TEX]tan(\frac{\pi}{4}-x).tan(\frac{\pi}{4}+x)=1[/TEX]
PT [TEX]\Leftrightarrow sin^42x+cos^42x=cos^44x[/TEX]
[TEX]\Leftrightarrow (sin^22x+cos^22x)-2sin^22xcos^22x=cos^44x[/TEX]
[TEX]\Leftrightarrow 1-\frac{1}{2}sin^24x=(1-sin^24x)^2[/TEX]
...giải bậc 2