[TẶNG BẠN] TRỌN BỘ Bí kíp học tốt 08 môn
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bài 8:cos3x+2−cos23x=2(1+sin22x)" role="presentation" style="font-family: "Open Sans", sans-serif; display: inline; line-height: normal; font-size: 14.6667px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">cos3x+2−cos23x−−−−−−−−−√=2(1+sin22x)cos3x+2−cos23x=2(1+sin22x)
ta có (cos3x+\sqrt{2-cos^23x)^2[/TEX]\leq4[tex]=>cos3x+\sqrt{2-cos^23x}" role="presentation" style="font-family: "Open Sans", sans-serif; display: inline; line-height: normal; font-size: 14.6667px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">(cos3x+\sqrt{2-cos^23x)^2[/TEX]\leq4[tex]=>cos3x+\sqrt{2-cos^23x}(cos3x+\sqrt{2-cos^23x)^2[/TEX]\leq4[tex]=>cos3x+\sqrt{2-cos^23x}\leq2 và 2(1+sin^22x)[/tex]\geq2 vậy pt có nghiệm khi và chỉ khi :[TEX]\left{\begin{cos3x=\sqrt{2-cos^23x}}\\{sin2x =0}" role="presentation" style="font-family: "Open Sans", sans-serif; display: inline; line-height: normal; font-size: 14.6667px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">2(1+sin^22x)[/tex]\geq2
vậy pt có nghiệm khi và chỉ khi :[TEX]\left{\begin{cos3x=\sqrt{2-cos^23x}}\\{sin2x =0}2(1+sin^22x)[/tex]\geq2 vậy pt có nghiệm khi và chỉ khi :[TEX]\left{\begin{cos3x=\sqrt{2-cos^23x}}\\{sin2x =0} \Leftrightarrow\left{\begin{cos3x\geq0}\\{cos^23x=2-cos^23x}\\{sin2x =0}" role="presentation" style="font-family: "Open Sans", sans-serif; display: inline; line-height: normal; font-size: 14.6667px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">\left{\begin{cos3x\geq0}\\{cos^23x=2-cos^23x}\\{sin2x =0}\left{\begin{cos3x\geq0}\\{cos^23x=2-cos^23x}\\{sin2x =0} \Leftrightarrow\left{cos3x=1}\\{sin2x =0}" role="presentation" style="font-family: "Open Sans", sans-serif; display: inline; line-height: normal; font-size: 14.6667px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">\left{cos3x=1}\\{sin2x =0}\left{cos3x=1}\\{sin2x =0} \Leftrightarrowx=2kπ" role="presentation" style="font-family: "Open Sans", sans-serif; display: inline; line-height: normal; font-size: 14.6667px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">x=2kπ[/TEX]
ta có (cos3x+\sqrt{2-cos^23x)^2[/TEX]\leq4[tex]=>cos3x+\sqrt{2-cos^23x}" role="presentation" style="font-family: "Open Sans", sans-serif; display: inline; line-height: normal; font-size: 14.6667px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">(cos3x+\sqrt{2-cos^23x)^2[/TEX]\leq4[tex]=>cos3x+\sqrt{2-cos^23x}(cos3x+\sqrt{2-cos^23x)^2[/TEX]\leq4[tex]=>cos3x+\sqrt{2-cos^23x}\leq2 và 2(1+sin^22x)[/tex]\geq2 vậy pt có nghiệm khi và chỉ khi :[TEX]\left{\begin{cos3x=\sqrt{2-cos^23x}}\\{sin2x =0}" role="presentation" style="font-family: "Open Sans", sans-serif; display: inline; line-height: normal; font-size: 14.6667px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">2(1+sin^22x)[/tex]\geq2
vậy pt có nghiệm khi và chỉ khi :[TEX]\left{\begin{cos3x=\sqrt{2-cos^23x}}\\{sin2x =0}2(1+sin^22x)[/tex]\geq2 vậy pt có nghiệm khi và chỉ khi :[TEX]\left{\begin{cos3x=\sqrt{2-cos^23x}}\\{sin2x =0} \Leftrightarrow\left{\begin{cos3x\geq0}\\{cos^23x=2-cos^23x}\\{sin2x =0}" role="presentation" style="font-family: "Open Sans", sans-serif; display: inline; line-height: normal; font-size: 14.6667px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">\left{\begin{cos3x\geq0}\\{cos^23x=2-cos^23x}\\{sin2x =0}\left{\begin{cos3x\geq0}\\{cos^23x=2-cos^23x}\\{sin2x =0} \Leftrightarrow\left{cos3x=1}\\{sin2x =0}" role="presentation" style="font-family: "Open Sans", sans-serif; display: inline; line-height: normal; font-size: 14.6667px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">\left{cos3x=1}\\{sin2x =0}\left{cos3x=1}\\{sin2x =0} \Leftrightarrowx=2kπ" role="presentation" style="font-family: "Open Sans", sans-serif; display: inline; line-height: normal; font-size: 14.6667px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">x=2kπ[/TEX]
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