3 câu hỏi là zì vậy

Kkkk

a)

\(7\sqrt{12}+\frac{1}{3}\sqrt{27}-\sqrt{75}\)

\(=14\sqrt{3}+\sqrt{3}-5\sqrt{3}\)

\(=10\sqrt{3}\)

b)

\(\left(2\sqrt{20}+\sqrt{125}-3\sqrt{80}\right):5\)

\(=\left(4\sqrt{5}+5\sqrt{5}-12\sqrt{5}\right):5\)

\(=-3\sqrt{5}:5\)

\(=\frac{-3\sqrt{5}}{5}\)

c)

\(3\sqrt{12a}-5\sqrt{3a}+\sqrt{48a}\)

\(=6\sqrt{3a}-5\sqrt{3a}+4\sqrt{3a}\)

\(=5\sqrt{3a}\)

2

a

\(\left|2x+7\right|+\left|2x-1\right|=\left|2x+7\right|+\left|1-2x\right|\ge\left|2x+7+1-2x\right|=8\)

Dấu "=" xảy ra tại \(-\frac{7}{2}\le x\le\frac{1}{2}\)

3

\(3a^2+4b^2=7ab\)

\(\Leftrightarrow3a^2-7ab+4b^2=0\)

\(\Leftrightarrow\left(3a^2-3ab\right)+\left(4b^2-4ab\right)=0\)

\(\Leftrightarrow3a\left(a-b\right)-4b\left(a-b\right)=0\)

\(\Leftrightarrow\left(3a-4b\right)\left(a-b\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}a=b\\3a=4b\end{cases}}\)

Làm nốt

\(\dfrac{ab}{a+3b+2c}=\dfrac{ab}{\left(a+c\right)+\left(b+c\right)+2b}\le\dfrac{1}{9}\left(\dfrac{ab}{a+c}+\dfrac{ab}{b+c}+\dfrac{ab}{2b}\right)\)

\(=\dfrac{1}{9}\left(\dfrac{ab}{a+c}+\dfrac{ab}{b+c}+\dfrac{a}{2}\right)\)

Tương tự:

\(\dfrac{bc}{b+3c+2a}\le\dfrac{1}{9}\left(\dfrac{bc}{a+b}+\dfrac{bc}{a+c}+\dfrac{b}{2}\right)\)

\(\dfrac{ac}{c+3a+2b}\le\dfrac{1}{9}\left(\dfrac{ac}{b+c}+\dfrac{ac}{a+b}+\dfrac{c}{2}\right)\)

Cộng vế:

\(P\le\dfrac{1}{9}\left(\dfrac{bc+ac}{a+b}+\dfrac{bc+ab}{a+c}+\dfrac{ab+ac}{b+c}+\dfrac{a+b+c}{2}\right)\)

\(P\le\dfrac{1}{9}.\left(a+b+c+\dfrac{a+b+c}{2}\right)=\dfrac{1}{2}\)

Dấu "=" xảy ra khi \(a=b=c=1\)

minh văn nguyễn

1C

6D

18D

20A

24A

29A

35D

31B

7...7...7=6

Trl:

7 - 7 : 7 = 6

quá vô lý à nha