Câu 8:

Giải:
Ta có: \(a:b=3:4\Rightarrow\frac{a}{3}=\frac{b}{4}\Rightarrow\frac{a^2}{9}=\frac{b^2}{16}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có:

\(\frac{a^2}{9}=\frac{b^2}{16}=\frac{a^2+b^2}{9+16}=\frac{36}{25}\)

+) \(\frac{a^2}{9}=\frac{36}{25}\Rightarrow a^2=\frac{324}{25}\Rightarrow a=\pm\frac{18}{5}\)

+) \(\frac{b^2}{16}=\frac{36}{25}\Rightarrow b^2=\frac{576}{25}\Rightarrow b=\pm\frac{24}{5}\)

Vậy bộ số \(\left(x;y\right)\) là \(\left(\frac{18}{5};\frac{24}{5}\right);\left(\frac{-18}{5};\frac{-24}{5}\right)\)

Ta có: 3636:(12x−91)=36

12x–91=3636:36

12x–91=101

12x=101+91

12x=192

x=192:12

x=16

Vậy x=16

440 + 2. (125 – x) = 546

2. (125 - x)=546 - 440

2. (125 - x)=106

125 - x=106 : 2

125 - x=53

x=125-53

x=72

a: \(3636:\left(12\cdot x-91\right)=36\)

=>\(12x-91=\frac{3636}{36}=101\)

=>12x=91+101=192

=>\(x=\frac{192}{12}=16\)

b: \(446+2\cdot\left(125-x\right)=546\)

=>\(2\left(125-x\right)=546-446=100\)

=>125-x=50

=>x=125-50=75

c: \(\left(x-36\right):18=10+2\)

=>\(\left(x-36\right):18=12\)

=>\(x-36=18\cdot12=216\)

=>x=216+36=252

\(\hept{\begin{cases}a+bc=501\\b+ca=501\\c+ab=501\end{cases}}\)\(\Rightarrow\)\(a+b+c=1503-\left(ab+bc+ca\right)\ge1503-\frac{\left(a+b+c\right)^2}{3}\)

\(\Rightarrow\)\(\left(a+b+c\right)^2+3\left(a+b+c\right)\ge4509\)

\(\Leftrightarrow\)\(\left(a+b+c+\frac{3}{2}\right)^2\ge\frac{18045}{4}\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}a+b+c\ge\frac{3\sqrt{2005}-3}{2}\\a+b+c\le\frac{-3\sqrt{2005}-3}{2}\end{cases}}\)

\(\Rightarrow\)\(\hept{\begin{cases}M=\frac{-\sqrt{18045}-3}{2}\left("="\Leftrightarrow a=b=c=\frac{\sqrt{2005}-1}{2}\right)\\m=\frac{\sqrt{18045}-3}{2}\left("="\Leftrightarrow a=b=c=\frac{-\sqrt{2005}-1}{2}\right)\end{cases}}\)

\(\Rightarrow\)\(M+2m=\frac{-3\sqrt{2005}-3+6\sqrt{2005}-6}{2}=\frac{3\sqrt{2005}-9}{2}\)

Mình xem đáp án thấy nó ghi là \(499-3\sqrt{2005}\)mà bạn.

dễ mà bạn suy nghĩ nhá

chiu dai the!!1

a: \(23\cdot37+13\)

=851+13

=864

b: 45-30:5

=45-6

=39

c: \(\left(7^2+3^8\right)-10^2\)

\(=49+6561-100\)

=6610-100

=6510

a) \(23 \times 37 + 13\)

\(23 \times 37 = 851 , 851 + 13 = 864\)

b) \(45 - 30 : 5\)

\(30 : 5 = 6 , 45 - 6 = 39\)

c) \(\left(\right. \frac{7}{27} + \frac{3}{8} \left.\right) - \frac{1}{10}\)

• Tìm mẫu chung:
  \(\frac{7}{27} + \frac{3}{8} = \frac{137}{216}\)
  \(\frac{137}{216} - \frac{1}{10} = \frac{577}{1080}\)

a) \(x+b+c=-3+\left(-4\right)+2=-5\)

b) \(x+b+c=0+7+\left(-8\right)=-1\)

a, Thay \(x=-3;b=-4;c=2\)vào biểu thức \(x+b+c\) ta có:

\(x+b+c=-3+\left(-4\right)+2\)

\(=-5\)

b, Thay \(x=0;b=7;c=-8\)vào biểu thức \(x+b+c\) ta có:

\(x+b+c=0+7+\left(-8\right)\)

\(=-1\)

a) , biết

b) biết

(-267)+(-33)=(-300)

a) \(-28 + (-10 ) = -( 28 + 10 ) = -38\)

b) \(-267+\left(-33\right)=-\left(267+33\right)=-300\)