chung minh cac he thuc sau

H

hothithuyduong

[TEX]a) (cotx)^2- (cosx)^2 =(cosx)^2.(cotx)^2[/TEX]

[TEX]VT = \frac{cos^2x}{sin^2x} - cos^2x = \frac{cos^2x - sin^2x.cos^2x}{sin^2x}[/TEX]

[TEX]= \frac{cos^2x(1 - sin^2x)}{sin^2x} = \frac{cos^2x}{sin^2x}.cos^2x = cos^2x.cot^2x = VP[/TEX]


[TEX]b) \frac{1}{1-sinx}+\frac{1}{1+sinx}= \frac{2}{cosx^2}[/TEX]


[TEX]VT = \frac{1 + sinx + 1 - sinx}{(1 - sinx)(1 + sinx)} = \frac{2}{1 - sin^2x} = \frac{2}{cos^2x} = VP[/TEX]
 
Top Bottom