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viquelinh


[TEX]1.Cosx + cos3x + cos5x + cos7x = 4[/TEX]
2. [TEX]\left{\begin{x+ y+ \sqrt {{x}^{2} - y^2 }= 0}\\{{y}\sqrt{{x}^{2} - {y}^{2}}=0}[/TEX]
3.[TEX]\left{\begin{2+ 6y = \frac{x}{y} - \sqrt{x - 2y}}\\{\sqrt{x +\sqrt{x-2y}}= x+ 3y -2}[/TEX]
2. [TEX]\left{\begin{x+ y+ \sqrt {{x}^{2} - y^2 }= 0}\\{{y}\sqrt{{x}^{2} - {y}^{2}}=0}[/TEX]
3.[TEX]\left{\begin{2+ 6y = \frac{x}{y} - \sqrt{x - 2y}}\\{\sqrt{x +\sqrt{x-2y}}= x+ 3y -2}[/TEX]
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