[toán 11] toán lượng giác

M

metla2011

[TEX]PT\Leftrightarrow x^2+2x.sin(xy)+sin^2(xy)+cos^2(xy)=0[/TEX]
[TEX]\Leftrightarrow [x+sin(xy)]^2+cos^2(xy)=0[/TEX]
[TEX]\Leftrightarrow \left{ x+sin(xy)=0\\cos(xy)=0[/TEX]
[TEX]\Leftrightarrow \left[ \left{x=-1\\y=\frac{-\pi}{2}+k2\pi \right. \\ \left{ x=1\\y=\frac{\pi}{2}+k2\pi \right. \right.(k \in Z)[/TEX]

:D:D:D
 
L

l94

[tex]x^2+2xsin(xy)+1=0[/tex]
[tex] \Leftrightarrow (x+sin(xy))^2+1-sin^2(xy)=0[/tex]
[tex] (x+sin(xy))^2 \geq 0[/tex]
[tex] 1-sin^2(xy)=cos^2(xy) \geq 0[/tex]
vậy [tex](x+sin(xy))^2=0[/tex]
và [tex]cos^2(xy)=0[/tex]
đến đây thì dễ rồi nhỉ?
 
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