. là phẩy hay nhân

nếu là phẩy

3,4+3,5=6,9

nếu là nhân

3.4+3.5=3.(4+5)=3.9=27

tổng a+b là 75 bạn nhé !

theo bđt cauchy ta có

\(\left\{{}\begin{matrix}\dfrac{a^2}{b}+b\ge2a\\\dfrac{b^2}{c}+c\ge2b\\\dfrac{c^2}{a}+a\ge2c\end{matrix}\right.\)

\(\Leftrightarrow\dfrac{a^2}{b}+\dfrac{b^2}{c}+\dfrac{c^2}{a}+a+b+c\ge2a+2b+2c\)

\(\Leftrightarrow\dfrac{a^2}{b}+\dfrac{b^2}{c}+\dfrac{c^2}{a}\ge a+b+c\)

\(\Rightarrow dpcm\)

C/M \(\dfrac{a}{bc}+\dfrac{b}{ca}+\dfrac{c}{ab}\ge\dfrac{1}{a}+\dfrac{1}{b}+\dfrac{1}{c}\)

theo bđt cosi ta có

\(\left\{{}\begin{matrix}\dfrac{a}{bc}+\dfrac{b}{ca}\ge2\sqrt{\dfrac{bc}{a^2bc}}=\dfrac{2}{a}\\\dfrac{a}{bc}+\dfrac{c}{ab}\ge\dfrac{2}{b}\\\dfrac{b}{ca}+\dfrac{c}{ab}\ge\dfrac{2}{c}\end{matrix}\right.\)

\(\Leftrightarrow2(\dfrac{a}{bc}+\dfrac{b}{ca}+\dfrac{c}{ab})\ge2(\dfrac{1}{a}+\dfrac{1}{b}+\dfrac{1}{c})\)

\(\Rightarrow dpcm\)

theo bđt cosi ta có

\(a^2+b^2\ge2ab\)\(\Leftrightarrow2a^2+2b^2\ge a^2+2ab+b^2\)

\(\Leftrightarrow2\left(a^2+b^2\right)\ge\left(a+b\right)^2\)

\(\Leftrightarrow\dfrac{a^2+b^2}{2}\ge\dfrac{\left(a+b\right)^2}{4}\)

\(\Leftrightarrow\sqrt{\dfrac{a^2+b^2}{2}}\ge\dfrac{a+b}{2}\)

\(\Rightarrow dpcm\)

5090 người

còn cách giải thì Nguyễn Ngọc Quý làm rùi đó

tick nhé

a)942-2567+2563-1942=(942-1942)+(2563-2567)=-1000-4=-1004

b)42.53+47.156-47.114=42.53+47(156-144)=42.53+47.42=42(47+53)

=42.100=4200

=\(26\left[2-\left(5-4^2\right)\right]=26\left[2-\left(5-16\right)\right]\)

\(=2.13\left(2--11\right)=2.13^2=2.169=338\)

suy ra x thuộc Ư(4)={-4;-2;-1;1;2;4}

vậy x thuộc {-4;-2;-1;1;2;4}