Cho <span class="MathJax_Preview" style="color: inherit;"><span class="MJXp-math" id="MJXp-Span-1"><span class="MJXp-mstyle" id="MJXp-Span-2"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-3">x</span><span class="MJXp-mo" id="MJXp-Span-4" style="margin-left: 0em; margin-right: 0.222em;">,</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-5">y</span></span></span></span><span id="MathJax-Element-1-Frame" class="mjx-chtml MathJax_CHTML MJXc-processed" tabindex="0" style="font-size: 127%;"><span id="MJXc-Node-1" class="mjx-math"><span id="MJXc-Node-2" class="mjx-mrow"><span id="MJXc-Node-3" class="mjx-mstyle"><span id="MJXc-Node-4" class="mjx-mrow" style="font-size: 144%;"><span id="MJXc-Node-5" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.298em;">x</span></span><span id="MJXc-Node-6" class="mjx-mo"><span class="mjx-char MJXc-TeX-main-R" style="margin-top: -0.145em; padding-bottom: 0.544em;">,</span></span><span id="MJXc-Node-7" class="mjx-mi MJXc-space1"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.495em; padding-right: 0.006em;">y</span></span></span></span></span></span></span><script type="math/tex" id="MathJax-Element-1">\Large x, y</script> là các số thực thỏa <span class="MathJax_Preview" style="color: inherit;"><span class="MJXp-math" id="MJXp-Span-6"><span class="MJXp-mstyle" id="MJXp-Span-7"><span class="MJXp-msubsup" id="MJXp-Span-8"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-9" style="margin-right: 0.05em;">x</span><span class="MJXp-mrow MJXp-script" id="MJXp-Span-10" style="vertical-align: 0.5em;"><span class="MJXp-mn" id="MJXp-Span-11">2</span></span></span><span class="MJXp-mo" id="MJXp-Span-12" style="margin-left: 0.267em; margin-right: 0.267em;">−</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-13">x</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-14">y</span><span class="MJXp-mo" id="MJXp-Span-15" style="margin-left: 0.267em; margin-right: 0.267em;">+</span><span class="MJXp-msubsup" id="MJXp-Span-16"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-17" style="margin-right: 0.05em;">y</span><span class="MJXp-mrow MJXp-script" id="MJXp-Span-18" style="vertical-align: 0.5em;"><span class="MJXp-mn" id="MJXp-Span-19">2</span></span></span><span class="MJXp-mo" id="MJXp-Span-20" style="margin-left: 0.333em; margin-right: 0.333em;">=</span><span class="MJXp-mn" id="MJXp-Span-21">1</span></span></span></span><span id="MathJax-Element-2-Frame" class="mjx-chtml MathJax_CHTML MJXc-processed" tabindex="0" style="font-size: 127%;"><span id="MJXc-Node-8" class="mjx-math"><span id="MJXc-Node-9" class="mjx-mrow"><span id="MJXc-Node-10" class="mjx-mstyle"><span id="MJXc-Node-11" class="mjx-mrow" style="font-size: 144%;"><span id="MJXc-Node-12" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-13" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.298em;">x</span></span></span><span class="mjx-sup" style="font-size: 70.7%; vertical-align: 0.513em; padding-left: 0px; padding-right: 0.071em;"><span id="MJXc-Node-14" class="mjx-texatom" style=""><span id="MJXc-Node-15" class="mjx-mrow"><span id="MJXc-Node-16" class="mjx-mn"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">2</span></span></span></span></span></span><span id="MJXc-Node-17" class="mjx-mo MJXc-space2"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.298em; padding-bottom: 0.445em;">−</span></span><span id="MJXc-Node-18" class="mjx-mi MJXc-space2"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.298em;">x</span></span><span id="MJXc-Node-19" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.495em; padding-right: 0.006em;">y</span></span><span id="MJXc-Node-20" class="mjx-mo MJXc-space2"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.298em; padding-bottom: 0.445em;">+</span></span><span id="MJXc-Node-21" class="mjx-msubsup MJXc-space2"><span class="mjx-base" style="margin-right: -0.006em;"><span id="MJXc-Node-22" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.495em; padding-right: 0.006em;">y</span></span></span><span class="mjx-sup" style="font-size: 70.7%; vertical-align: 0.513em; padding-left: 0.082em; padding-right: 0.071em;"><span id="MJXc-Node-23" class="mjx-texatom" style=""><span id="MJXc-Node-24" class="mjx-mrow"><span id="MJXc-Node-25" class="mjx-mn"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">2</span></span></span></span></span></span><span id="MJXc-Node-26" class="mjx-mo MJXc-space3"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.101em; padding-bottom: 0.298em;">=</span></span><span id="MJXc-Node-27" class="mjx-mn MJXc-space3"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">1</span></span></span></span></span></span></span><script type="math/tex" id="MathJax-Element-2">\Large x^{2} - xy + y^{2} = 1</script>.

Cho x,yx,y là các số thực thỏa x2xy+y2=1x2xy+y2=1.

4.3/5

Tác giả: Thầy Tùng

Đăng ngày: 18 Aug 2022

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Câu hỏi:

Cho x,yx,y là các số thực thỏa x2xy+y2=1x2xy+y2=1. Gọi M,mM,m lần lượt là giá trị lớn nhất, giá trị nhỏ nhất của P=x4+y4+1x2+y2+1P=x4+y4+1x2+y2+1. Giá trị của A=M+15mA=M+15m là:

Đáp án án đúng là: B

Lời giải chi tiết:

Chọn B

Ta có:

x2xy+y2=13xy+1=(x+y)20xy13x2xy+y2=13xy+1=(x+y)20xy13

x2xy+y2=1xy=1(xy)21xy1x2xy+y2=1xy=1(xy)21xy1

Đặt t=xyt=xy với 13t113t1.

Theo đề bài ta có: x2+y2=1+tx2+y2=1+t.

P=t2+2t+2t+2=f(t)P=t2+2t+2t+2=f(t)

f(t)=t24t+2(t+2)2=0

f(t)=0[t=2+6[13;1]t=26[13;1]

Ta có:

f(13)=1115;

f(1)=1; 

f(62)=626

Khi đó:

M=626m=1115

M+15m=626+15.1115=1726