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niemkieuloveahbu

[TEX]sin^3x+cos^3x=2-sin^4x[/TEX]

[TEX]VT= sin^3x+cos^3x \leq sin^2x+cos^2x=1\\ VT =2-sin^4x \geq 1\\ Dau\ "=" \Leftrightarrow \left{sin^4x=1\\sin^3x=sin^2x\\cos^3x=cos^2x[/TEX]
 
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