1) Cho a,b,ca,b,c là các số thực dương thoả: abc=1abc=1. Cmr:aba5+b5+ab+bcb5+c5+bc+cac5+a5+ca≤1aba5+b5+ab+bcb5+c5+bc+cac5+a5+ca≤12) Cho a,b,ca,b,c là các số thực dương thoả mãn: a2+b2+c2=1a2+b2+c2=1. Tìm giả trị nhỏ nhất của:abc+bca+cababc+bca+cab3) Cho a≥6a≥6. CMR: a2+6√a−√6≥36a2+6a−6≥364) Cho a,b,c,da,b,c,d là các số nguyên và 1≤a≤b≤c≤d≤901≤a≤b≤c≤d≤90. Tìm giá trị nhỏ nhất...
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1) Cho a,b,c" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">a,b,c là các số thực dương thoả: abc=1" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">abc=1. Cmr:
aba5+b5+ab+bcb5+c5+bc+cac5+a5+ca≤1" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">aba5+b5+ab+bcb5+c5+bc+cac5+a5+ca≤1
2) Cho a,b,c" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">a,b,c là các số thực dương thoả mãn: a2+b2+c2=1" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">a2+b2+c2=1. Tìm giả trị nhỏ nhất của:
abc+bca+cab" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">abc+bca+cab
3) Cho a≥6" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">a≥6. CMR: a2+6a−6≥36" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">a2+6√a−√6≥36
4) Cho a,b,c,d" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">a,b,c,d là các số nguyên và 1≤a≤b≤c≤d≤90" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">1≤a≤b≤c≤d≤90. Tìm giá trị nhỏ nhất của: P=ab+3cd" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">P=ab+3cd
5) Cho các số thực dương x,a,b,c" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">x,a,b,c thoả điều kiện: x2=a2+b2+c2" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">x2=a2+b2+c2.
CMR: ax+2a+bx+2b+c2+2c≤32+3" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">ax+2a+bx+2b+c2+2c≤32+√3
6) Tìm giá trị lớn nhất và nhỏ nhất của hàm số:
y=2+2sin⁡(x+Π4)+21+sin⁡x+cos⁡x+sin⁡xcos⁡x" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">y=2+√2sin(x+Π4)+2√1+sinx+cosx+sinxcosx, với x∈R" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">x∈R
7) Cho x>0" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">x>0, y>0" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">y>0 và x+2y<5Π4" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">x+2y<5Π4. CMR:
cos⁡(x+y)<ysin⁡xxsin⁡y" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">cos(x+y)<ysinxxsiny
8) Cho các số α,β,γ" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">α,β,γ thoả mãn: α+β+γ=Π2" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">α+β+γ=Π2
Tính giá trị nhỏ nhất của biểu thức:
A=tan⁡αtan⁡β+1+tan⁡βtan⁡γ+1+tan⁡γtan⁡α+1" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; overflow-wrap:normal; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal" class="MathJax_CHTML mjx-chtml">A=√tanαtanβ+1+√tanβtanγ+1+√tanγtanα+1
bài 2
A B C O H K J
ta có \(\overrightarrow{AO}.\left(\overrightarrow{BO}+\overrightarrow{AC}-2\overrightarrow{BC}\right)=\overrightarrow{AO}.\overrightarrow{BO}+\overrightarrow{AO}.\overrightarrow{AC}-\overrightarrow{AO}.2\overrightarrow{BC}\)
\(=\overrightarrow{AO}.\overrightarrow{BO}+\overrightarrow{AO}.\overrightarrow{AC}=AO.BO.cos\left(120^0\right)+AO.AC.cos\left(30^0\right)\)
\(=\frac{a\sqrt{3}}{3}.\frac{a\sqrt{3}}{3}.-\frac{1}{2}+\frac{a\sqrt{3}}{3}.a.\frac{\sqrt{3}}{2}=\frac{a^2}{3}\)
b.Gọi J là trung điểm CK
ta có \(\overrightarrow{MA}+\overrightarrow{MB}+2\overrightarrow{MC}=2\overrightarrow{MK}+2\overrightarrow{MC}=4\overrightarrow{MJ}\)
do \(\left|4\overrightarrow{MJ}\right|=a\Leftrightarrow MJ=\frac{a}{4}\)vậy tập hợp M là các điểm nằm trên đường tròn tâm J bán kính a/4.
Bài 3. điều kiện \(x\ge1\)
đặt \(\sqrt{x-1}=a\ge0\) ta có
\(a^2+a+3=3\sqrt{a^3+1}\)
hay \(\left(a^2-a+1\right)+2\left(a+1\right)=3\sqrt{\left(a^2-a+1\right).\left(a+1\right)}\)
\(\Leftrightarrow\left(\sqrt{a^2-a+1}-\sqrt{a+1}\right)\left(\sqrt{a^2-a+1}-2\sqrt{a+1}\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}a^2-a+1=a+1\\a^2-a+1=4\left(a+1\right)\end{cases}\Leftrightarrow\orbr{\begin{cases}a=0\\a=2\end{cases}}}\) hoặc \(a=\frac{5+\sqrt{37}}{2}\)
từ đó ta tìm được x thuộc tập \(S=\left\{1;5;\frac{33+5\sqrt{37}}{2}\right\}\)