[toán 10] lượng giác

H

hn3

Câu 1 :

[TEX]M=tan9^0-tan27^0-tan63^0+tan81^0[/TEX]

[TEX]M=(tan9+tan81)-(tan27+tan63)[/TEX]

[TEX]M=\frac{sin(9+81)}{cos9.cos81}-\frac{sin(27+63)}{cos27.cos63}[/TEX]

[TEX]M=\frac{1}{cos9.sin9}-\frac{1}{cos27.sin27}[/TEX]

[TEX]M=\frac{2}{sin18}-\frac{2}{sin54}=\frac{2(sin54-sin18)}{sin54.sin18}[/TEX]

[TEX]M=\frac{2.2.cos36.sin18}{sin54.sin18}=4[/TEX]

:p
 
You must log in or register to reply here.
Top Bottom