

Chứng minh
[tex]\frac{cot^{2}x-cot^{2}y}{cot^{2}x*cot^{2}y}=\frac{cos^{2}x-cos^{2}y}{cos^{2}x*cos^{2}y}[/tex]
[tex]\frac{1-sin2x}{1+sin2x}=cot^{2}x(\frac{pi}{4}+x)[/tex]
[tex]\frac{cot^{2}x-cot^{2}y}{cot^{2}x*cot^{2}y}=\frac{cos^{2}x-cos^{2}y}{cos^{2}x*cos^{2}y}[/tex]
[tex]\frac{1-sin2x}{1+sin2x}=cot^{2}x(\frac{pi}{4}+x)[/tex]
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