[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

x2+2xsin(xy)+1=0x^2+2xsin(xy)+1=0
⇔(x+sin(xy))2+1−sin2(xy)=0 \Leftrightarrow (x+sin(xy))^2+1-sin^2(xy)=0
(x+sin(xy))2≥0 (x+sin(xy))^2 \geq 0
1−sin2(xy)=cos2(xy)≥0 1-sin^2(xy)=cos^2(xy) \geq 0
vậy (x+sin(xy))2=0(x+sin(xy))^2=0
và cos2(xy)=0cos^2(xy)=0
đến đây thì dễ rồi nhỉ?
 
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