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AH
Akai Haruma
Giáo viên
26 tháng 6 2019

Lời giải:

\(\sqrt{1+2017^2+\frac{2017^2}{2018^2}}+\frac{2017}{2018}\)

\(=\sqrt{(1+2017)^2-2.2017+\frac{2017^2}{2018^2}}+\frac{2017}{2018}\)

\(\sqrt{2018^2-2.2018.\frac{2017}{2018}+\frac{2017^2}{2018^2}}+\frac{2017}{2018}\)

\(=\sqrt{(2018-\frac{2017}{2018})^2}+\frac{2017}{2018}=2018-\frac{2017}{2018}+\frac{2017}{2018}=2018\)

11 tháng 9 2019

Đặt \(2017=a\)

=>\(2018=a+1\)

Với mọi \(a\in N\) có:\(\sqrt{1+a^2+\frac{a^2}{\left(a+1\right)^2}}=\sqrt{\frac{\left(a+1\right)^2+a^2\left(a+1\right)^2+a^2}{\left(a+1\right)^2}}=\sqrt{\frac{a^2+2a+1+a^2\left(a^2+2a+1\right)+a^2}{\left(a+1\right)^2}}=\sqrt{\frac{2a^2+2a+1+a^4+2a^3+a^2}{\left(a+1\right)^2}}=\sqrt{\frac{\left(a^4+2a^2+1\right)+2a\left(a^2+1\right)+a^2}{\left(a+1\right)^2}}\)

=\(\sqrt{\frac{\left(a^2+1\right)^2+2a\left(a^2+1\right)+a^2}{\left(a+1\right)^2}}=\sqrt{\frac{\left(a^2+a+1\right)}{\left(a+1\right)^2}}=\left|\frac{a^2+a+1}{a+1}\right|\)(do \(a\ge0\))

=\(\frac{a\left(a+1\right)+1}{a+1}=a+\frac{1}{a+1}\)

=> \(\sqrt{1+a^2+\frac{a^2}{\left(a+1\right)^2}}=a+\frac{1}{a+1}\)

Thay a=2017 có:

\(\sqrt{1+2017^2+\left(\frac{2017}{2018}\right)^2}=2017+\frac{1}{2017+1}=2017+\frac{1}{2018}\)

=>\(\sqrt{1+22017^2+\left(\frac{2017}{2018}\right)^2}+\frac{2017}{2018}=2017+\frac{1}{2018}+\frac{2017}{2018}\)

<=> M=2017+1=2018

Vậy M=2018

Vũ Minh Tuấn Lê Thị Thục Hiền @No choice teen

2 tháng 9 2017

\(\sqrt{1+a^2+\left(\frac{a}{a+1}\right)^2}\)=\(\sqrt{\frac{\left(a+1\right)^2+a^2.\left(a+1\right)^2+a^2}{\left(a+1\right)^2}}\) =\(\sqrt{\frac{a^2\left(a^2+2a+1+1\right)+\left(a+1\right)^2}{\left(a+1\right)^2}}\)

=\(\sqrt{\frac{a^4+2a^2.\left(a+1\right)+\left(a+1\right)^2}{\left(a+1\right)^2}}\) =\(\sqrt{\frac{\left(a^2+a+1\right)^2}{\left(a+1\right)^2}}=\frac{a^2+a+1}{a+1}=\frac{a\left(a+1\right)+1}{a+1}=a+\frac{1}{a+1}\)

thay vao dau bai ta co 

\(2017+\frac{1}{2018}+\frac{2017}{2018}=2017+1=2018\)

31 tháng 3 2018

khó quá nhỉ

22 tháng 5 2020

Câu b đề sai nha, bây giờ đặt \(a=\sqrt{2017},b=\sqrt{2018}\)

Ta có \(\frac{a^2}{b}+\frac{b^2}{a}< a+b\Leftrightarrow ab\left(\frac{a^2}{b}+\frac{b^2}{a}\right)< ab\left(a+b\right)\)

\(\Leftrightarrow a^3+b^3< ab\left(a+b\right)\)(1)

Mà \(ab\left(a+b\right)\le\left(a^2-ab+b^2\right)\left(a+b\right)=a^3+b^3\)(2)

Từ (1), (2) => Sai

22 tháng 5 2020

a) Ta có:

\(\frac{1}{\left(k+1\right)\sqrt{k}}=\frac{k+1-k}{\left(k+1\right)\sqrt{k}}=\frac{\left(\sqrt{k+1}+\sqrt{k}\right)\left(\sqrt{k+1}-\sqrt{k}\right)}{\left(k+1\right)\sqrt{k}}\)\(< \frac{2\sqrt{k+1}\left(\sqrt{k+1}-\sqrt{k}\right)}{\left(k+1\right)\sqrt{k}}=\frac{2\left(\sqrt{k+1}-\sqrt{k}\right)}{\sqrt{k+1}\sqrt{k}}=\frac{2}{\sqrt{k}}-\frac{2}{\sqrt{k+1}}\)

Cho k=1,2,....,n rồi cộng từng vế ta có:

\(\frac{1}{2}+\frac{1}{3\sqrt{2}}+\frac{1}{4\sqrt{3}}+....+\frac{1}{\left(n+1\right)\sqrt{n}}< \left(\frac{2}{\sqrt{1}}-\frac{2}{\sqrt{2}}\right)+\left(\frac{2}{\sqrt{2}}-\frac{2}{\sqrt{3}}\right)\)\(+\left(\frac{2}{\sqrt{3}}-\frac{2}{\sqrt{4}}\right)+....+\left(\frac{2}{\sqrt{n}}-\frac{2}{\sqrt{n+1}}\right)=2-\frac{2}{\sqrt{n-1}}< 2\)

16 tháng 10 2018

\(B=\sqrt{1+2017^2+\frac{2017^2}{2018^2}}+\frac{2017}{2018}\)

\(B=\sqrt{\left(1+2.2017+2017^2\right)-2.2017+\frac{2017^2}{2018^2}}+\frac{2017}{2018}\)

\(B=\sqrt{\left(1+2017\right)^2-2.2017+\frac{2017^2}{2018^2}}+\frac{2017}{2018}\)

\(B=\sqrt{2018^2-2.2017+\frac{2017^2}{2018^2}}+\frac{2017}{2018}\)

\(B=\sqrt{\left(2018-\frac{2017}{2018}\right)^2}+\frac{2017}{2018}\)

Mà  \(\frac{2017}{2018}< 1\Rightarrow2018-\frac{2017}{2018}>0\)

\(\Rightarrow B=2018-\frac{2017}{2018}+\frac{2017}{2018}\)

\(B=2018\)

Vậy bt B có giá trị nguyên 

16 tháng 10 2018

Cảm ơn bạn mk vừa đăng lên thì đã thấy luôn cách giải 😂

21 tháng 1 2020

Áp dụng bđt Svacxo ta có :

\(\dfrac{2017}{\sqrt{2018}}+\dfrac{2018}{\sqrt{2017}}\ge\dfrac{\left(\sqrt{2017}+\sqrt{2018}\right)^2}{\sqrt{2018}+\sqrt{2017}}=\sqrt{2017}+\sqrt{2018}\)

Dấu bằng xảy ra khi:

\(\dfrac{2017}{\sqrt{2018}}=\dfrac{2018}{\sqrt{2017}}\Leftrightarrow2017=2018\left(vl\right)\)

Suy ra không xảy ra dấu bằng

Vậy \(\dfrac{2017}{\sqrt{2018}}+\dfrac{2018}{\sqrt{2017}}>\sqrt{2017}+\sqrt{2018}\)

27 tháng 7 2019

\(\frac{2017}{\sqrt{2018}}+\frac{2018}{\sqrt{2017}}=\frac{2017\sqrt{2017}+2018\sqrt{2018}}{\sqrt{2017}\cdot\sqrt{2018}}\)

\(=\left(\sqrt{2017}+\sqrt{2018}\right)\cdot\frac{2017+2018-\sqrt{2018\cdot2017}}{\sqrt{2017\cdot2018}}\)

Ta thấy \(\frac{2017+2018-\sqrt{2018\cdot2017}}{\sqrt{2018\cdot2017}}=\frac{\sqrt{2017}}{\sqrt{2018}}+\frac{\sqrt{2018}}{\sqrt{2017}}-1\)

Áp dụng ĐBT Cô si thì \(\frac{\sqrt{2017}}{\sqrt{2018}}+\frac{\sqrt{2018}}{\sqrt{2017}}\ge2\Rightarrow\frac{\sqrt{2017}}{\sqrt{2018}}+\frac{\sqrt{2018}}{\sqrt{2017}}-1\ge1\)

\(\Rightarrow\sqrt{2017}+\sqrt{2018} < \frac{2017}{\sqrt{2018}}+\frac{2018}{\sqrt{2017}}\)