\(\frac{x+2015}{5}+\frac{x+2016}{4}=\frac{x+2017}{3}+\frac{x+2018}{2}\)

\(\Leftrightarrow\left(\frac{x+2015}{5}+1\right)+\left(\frac{x+2016}{4}+1\right)=\left(\frac{x+2017}{3}+1\right)+\left(\frac{x+2018}{2}+1\right)\)

\(\Leftrightarrow\frac{x+2020}{5}+\frac{x+2020}{4}-\frac{x+2020}{3}-\frac{x+2020}{2}=0\)

\(\Leftrightarrow\left(x+2020\right)\left(\frac{1}{5}+\frac{1}{4}-\frac{1}{3}-\frac{1}{2}\right)=0\)

\(\Leftrightarrow x+2020=0\)vì \(\frac{1}{5}+\frac{1}{4}+\frac{1}{3}+\frac{1}{2}\ne0\)

\(\Leftrightarrow x=-2020\)

khó lắm

bây h thì bạn giải đc chưa

Cảm ơn bạn rất nhiều mình đã hiểu rồi 

Chúc bạn học tốt nhé

\(\left(3x+1\right)^2=25\)

\(\Rightarrow\left(3x+1\right)^2=5^2=\left(-5\right)^2\)

\(\Rightarrow\orbr{\begin{cases}3x+1=5\\3x+1=-5\end{cases}\Rightarrow\orbr{\begin{cases}3x=5-1=4\\3x=-5-1=-6\end{cases}}}\Rightarrow\orbr{\begin{cases}x=\frac{4}{3}\\x=-2\end{cases}}\)

\(\left[x-\frac{1}{2}\right]+\frac{1}{2}=\frac{5}{8}\)

\(\Rightarrow x-0=\frac{5}{8}\)

\(x=\frac{5}{8}\)

\(\left[x+\frac{3}{4}\right]-\frac{1}{3}=0\)

\(x+\frac{3}{4}=0+\frac{1}{3}=\frac{1}{3}\)

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

\(x=\frac{-5}{12}\)

\(\frac{1}{9}.3^4.3x=3^7\)

\(\Rightarrow\frac{1}{9}.3^5x=3^7\)

\(x=3^7:\frac{1}{9}:3^5\)

\(x=3^2.9\)

\(x=81\)

\(\frac{x}{5}=\frac{4}{21}\)

\(\Rightarrow21x=4.5\)

\(\Rightarrow x=\frac{4.5}{21}\)

\(x=\frac{20}{21}\)

\(a.\) \(25,4-\frac{1}{4}\div x+1250\%=37,5\)

 \(25,4-0.25\div x+12,5=37,5\)

\(25,4-0,25\div x=37,5-12,5\)

\(25,4-0,25\div x=25\)

\(0,25\div x=25,4-25\)

\(0,25\div x=0,4\)

\(x=0,25\div0,4\)

\(x=0,625\)

\(b.\)\(3\frac{1}{8}\div\left(\frac{2}{5}-x\right)\times\frac{8}{25}=3\)

\(\frac{3\times8+1}{8}\div\left(\frac{2}{5}-x\right)=3\div\frac{8}{25}\)

\(\frac{25}{8}\div\left(\frac{2}{5}-x\right)=\frac{75}{8}\)

\(\frac{2}{5}-x=\frac{25}{8}\div\frac{75}{8}\)

\(\frac{2}{5}-x=\frac{25}{8}\times\frac{8}{75}\)

\(\frac{2}{5}-x=\frac{1}{3}\)

\(x=\frac{2}{5}-\frac{1}{3}=\frac{6}{15}-\frac{5}{15}\)

\(x=\frac{1}{15}\)

a)25,4-\(\frac{1}{4}\): x +1250%=37,5

25,4 - 0,25 : x + 12,5 = 37,5

25,4 - 0,25 : x            =37,5 -12,5

25,4 - 0,25 : x            = 25

         0,25 : x            = 25,4 -25

         0,25 : x            =       0,4

                  x            = 0,25;0,4

                  x            =   0,625

b) \(3\frac{1}{8}:\left(\frac{2}{5}-x\right)\times\frac{8}{25}=3\)

\(3,125:\left(0,4-x\right)\times0,32=3\)

\(3,125:\left(0,4-x\right)=3:0,32\)

\(3,125:\left(0,4-x\right)=9,375\)

\(0,4-x=3,125:9,375\)

\(0,4-x=\frac{1}{3}\)

\(x=0,4-\frac{1}{3}\)

\(x=\frac{1}{15}\)

có chỗ x^7 hả

a) B=(\(\frac{21}{x^2-9}\)-\(\frac{x-4}{3-x}\)-\(\frac{x-1}{3+x}\)) : (1-\(\frac{1}{x+3}\)) (ĐK: x khác +-3)

=(\(\frac{21}{\left(x-3\right).\left(x+3\right)}\)+\(\frac{x-4}{x-3}\)-\(\frac{x-1}{x+3}\)) : (1-\(\frac{1}{x+3}\))

=(\(\frac{21+\left(x+4\right).\left(x+3\right)-\left(x-1\right).\left(x-3\right)}{\left(x-3\right).\left(x+3\right)}\):(\(\frac{x+3-1}{x+3}\))

=(\(\frac{3x+6}{\left(x-3\right).\left(x+3\right)}\)) . (\(\frac{x+3}{x+2}\))

=(\(\frac{3.\left(x+2\right)}{\left(x-3\right).\left(x+3\right)}\). \(\frac{x+3}{x+2}\)

=\(\frac{3}{x-3}\)

b) B=\(\frac{3}{x-3}\)=\(\frac{-3}{5}\)

(=) \(\frac{3.5}{x-3}\)=-3

(=) -3.(x-3) = 15

(=) -3x=6

(=) x=-2

vậy x=2 thì B=\(\frac{-3}{5}\)

c) B=\(\frac{3}{x-3}\)<0

(=) 3 < x - 3

(=) -x < - 3 - 3

(=) x > 6

Vậy với x > 6 thì B < 0

\(B=\left(\frac{21}{x^2-9}-\frac{x-4}{3-x}-\frac{x-1}{x+3}\right):\left(1-\frac{1}{x+3}\right)\)

\(B=\left[\frac{21}{\left(x-3\right)\left(x+3\right)}+\frac{\left(x-4\right)\left(x+3\right)}{\left(x-3\right)\left(x+3\right)}-\frac{\left(x-1\right)\left(x-3\right)}{\left(x+1\right)\left(x+3\right)}\right]\)    \(:\left[\frac{x+3-1}{x+3}\right]\)

\(B=\frac{21+x^2-x-12-x^2+4x-3}{\left(x-3\right)\left(x+3\right)}:\frac{x+2}{x+3}\)

\(B=\frac{3x+6}{\left(x-3\right)\left(x+3\right)}.\frac{x+3}{x+2}\)

\(B=\frac{3.\left(x+2\right)}{\left(x-3\right)\left(x+3\right)}.\frac{x+3}{x+2}\)

\(B=\frac{3}{x-3}\)

b)   \(B=\frac{-3}{5}\Leftrightarrow\frac{3}{x-3}=\frac{-3}{5}\)

\(\Leftrightarrow-3x+9=15\)

\(\Leftrightarrow-3x=6\)

\(\Leftrightarrow x=-2\)

vậy....

c) \(B< 0\Leftrightarrow\frac{3}{x-3}< 0\)

\(\Leftrightarrow x-3< 0\)   vì \(3>0\)

\(\Leftrightarrow x< 3\)

vậy....