1/4 . x - (x - 4/5) - 1/2 = 2x - 6

1/4 x - x + 4/5 - 1/2 = 2x - 6

1/4 x - x - 2x = -6 - 4/5 + 1/2

-11/4 x = -63/10

x = -63/10 : (-11/4)

x = 126/55

x = 126/55

\(a)\) \(2x-5=21\)

\(\Leftrightarrow\) \(2x=21+5\)

\(\Leftrightarrow\) \(2x=26\)

\(\Leftrightarrow\) \(x=26:2\)

\(\Leftrightarrow\) \(=13\)

\(b)\) \(\frac{3}{4}+\frac{1}{4}x=\frac{5}{6}\)

\(\Leftrightarrow\) \(\frac{1}{4}x=\frac{5}{6}-\frac{3}{4}\)

\(\Leftrightarrow\) \(\frac{1}{4}x=\frac{1}{12}\)

\(\Leftrightarrow\) \(x=\frac{1}{3}\)

a, \(A=\left|x+2\right|+3\ge3\)

dấu "=" xảy ra\(\Leftrightarrow x=-2\)

Vậy \(A_{min}=3\Leftrightarrow x=-2\)

b,\(B=5+\left|2x-7\right|\ge5\)

dấu "=" xảy ra\(\Leftrightarrow x=\dfrac{7}{2}\)

Vậy \(B_{min}=5\Leftrightarrow x=\dfrac{7}{2}\)

c, \(-\left|4x+5\right|+1\le1\)

dấu "=" xảy ra\(\Leftrightarrow x=-\dfrac{5}{4}\)

Vậy \(C_{max}=1\Leftrightarrow x=-\dfrac{5}{4}\)

d, \(D=3-\left|x+3\right|\le3\)

dấu "=" xảy ra\(\Leftrightarrow x=-3\)

Vậy \(D_{max}=3\Leftrightarrow x=-3\)

Câu 2:

a: x-158=32

=>x=158+32

=>x=190

b: \(x\cdot24=264\)

=>\(x=\dfrac{264}{24}\)

=>x=11

c: \(6x+9=3^7:3^4\)

=>\(6x+9=3^3\)

=>6x+9=27

=>6x=18

=>x=18/6=3

Câu 1:

a: \(86\cdot19+14\cdot19\)

\(=19\left(86+14\right)\)

\(=19\cdot100=1900\)

b: \(4\cdot\left(-5\right)^2-104\cdot\left(-5\right)^2\)

\(=4\cdot25-104\cdot25\)

\(=25\left(4-104\right)=-100\cdot25=-2500\)

c: \(7\cdot\left(-2\right)\cdot8\left(-5\right)\)

\(=7\cdot2\cdot8\cdot5\)

\(=56\cdot10=560\)

d: \(59-\left[59+\left(-76\right)\right]\)

\(=59-59+76\)

=76

Bài 3: 

\(\Leftrightarrow x^3+64-x^3+25x=264\)

hay x=8

\(1,C=6x^2+23x-55-6x^2-23x-21=-76\\ 2,=\left(2x^4-x^2+2x^3-x-6x^2+6-3\right):\left(2x^2-1\right)\\ =\left[\left(2x^2-1\right)\left(x^2+x-6\right)-3\right]:\left(2x^2-1\right)\\ =x^2+x-6\left(dư.-3\right)\\ 3,\Leftrightarrow x^3+64-x^3+25x=264\\ \Leftrightarrow25x=200\Leftrightarrow x=8\)

\(\dfrac{4\times x}{1\times5}\) + \(\dfrac{4\times x}{5\times9}\) + \(\dfrac{4\times x}{9\times13}\) + \(\dfrac{4\times x}{13\times17}\) = 16

\(x\times\left(\dfrac{4}{1\times5}+\dfrac{4}{5\times9}+\dfrac{4}{9\times13}+\dfrac{4}{13\times17}\right)\) = 16

\(x\) \(\times\) (\(\dfrac{1}{1}\) - \(\dfrac{1}{5}\) + \(\dfrac{1}{5}\) - \(\dfrac{1}{9}\) + \(\dfrac{1}{9}\) - \(\dfrac{1}{13}\) + \(\dfrac{1}{13}\) - \(\dfrac{1}{17}\)) = 16

\(x\) \(\times\) ( \(\dfrac{1}{1}\) - \(\dfrac{1}{17}\)) = 16

\(x\) \(\times\) \(\dfrac{16}{17}\)  = 16

\(x\)            = 16 : \(\dfrac{16}{17}\)

\(x\)             = 17