KHO THE

\(A=\frac{\left[\left(25-1\right):1+1\right]\left(25+1\right)}{2}=325.\)

\(B=\frac{\left[\left(51-3\right):2+1\right]\left(51+3\right)}{2}=675\)

\(C=\frac{\left[\left(81-1\right):4+1\right]\left(81+1\right)}{2}=861\)

1 A great deal of tea is drunk in England

3 Her dog is often taken for a walk by her

4 English is spoken all over the world

5 Their friends have been met at the railway station by a group of students

6 Tom wasn't allowed to take these books home

7 Exercises won't be corrected by the teacher tomorrow

8 How many trees were cut down to built that fence?

9 Many people are attracted by this well-known library

10 He likes being called "sir"

11 My bike can't be repaired by him

12 Tom has been operated by Mary since 10 o'clock

13 We have been taught French by Mr Smith for 2 years

14 The children weren't looked after properly 

1 A great deal of tea is drunk in England

3 Her dog is often taken for a walk by her

4 English is spoken all over the world

5 Their friends have been met at the railway station by a group of students

6 Tom wasn't allowed to take these books home

7 Exercises won't be corrected by the teacher tomorrow

8 How many trees were cut down to built that fence?

9  Many people are attracted by this well-known library

10 He likes being called "sir"

11 My bike can't be repaired by him

12 Tom has been operated by Mary since 10 o'clock

13 We have been taught French by Mr Smith for 2 years

14 The children weren't looked after properly 

a: \(\dfrac{x}{6}=\dfrac{8}{3}\)

=>\(x=6\cdot\dfrac{8}{3}=\dfrac{6}{3}\cdot8=8\cdot2=16\)

b: \(\dfrac{5}{x}=\dfrac{4}{9}\)

=>\(x=\dfrac{5\cdot9}{4}=\dfrac{45}{4}\)

c: \(\dfrac{x+3}{-4}=\dfrac{5}{20}\)

=>\(x+3=\dfrac{-4\cdot5}{20}=-1\)

=>x=-1-3=-4

d: \(\dfrac{7}{3+4x}=\dfrac{-2}{9}\)

=>\(4x+3=\dfrac{9\cdot7}{-2}=-\dfrac{63}{2}\)

=>\(4x=-\dfrac{63}{2}-3=-\dfrac{69}{2}\)

=>\(x=-\dfrac{69}{8}\)

f: ĐKXĐ: x<>1

\(\dfrac{3}{x-1}=\dfrac{x-1}{27}\)

=>\(\left(x-1\right)^2=3\cdot27=81\)

=>\(\left[{}\begin{matrix}x-1=9\\x-1=-9\end{matrix}\right.\)

=>\(\left[{}\begin{matrix}x=10\left(nhận\right)\\x=-8\left(nhận\right)\end{matrix}\right.\)

7/5 + 8/5( x+1)= 3

         8/5(x+1) = 3 - 7/5

         8/5(x+1) = 8/5

           x+1 = 8/5:8/5

           x+1 = 1

    => x = 1-1 = 0

Vậy x = 0

x=0

\(\dfrac{7}{5}+\dfrac{8}{5}.\left(x+1\right)=3\\ \dfrac{8}{5}.\left(x+1\right)=3-\dfrac{7}{5}=\dfrac{8}{5}.\left(x+1\right)=\dfrac{8}{5}\\ x+1=\dfrac{8}{5}:\dfrac{8}{5}\\ x+1=1\\ \Rightarrow x=0\)

c: \(\left(x^2-2x\right)\left(x^2-2x-1\right)-12\)

\(=\left(x^2-2x\right)^2-\left(x^2-2x\right)-12\)

\(=\left(x^2-2x\right)^2-4\left(x^2-2x\right)+3\left(x^2-2x\right)-12\)

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

a) \(\dfrac{1}{4}-3\left(\dfrac{1}{12}+\dfrac{3}{8}\right)=\dfrac{1}{4}-\dfrac{1}{4}-\dfrac{9}{8}=-\dfrac{9}{8}\)

b) \(\left(-\dfrac{2}{3}+\dfrac{3}{5}\right):\dfrac{1}{50}-30=\left(-\dfrac{2}{3}+\dfrac{3}{5}\right).50-30=-\dfrac{100}{3}+30-30=-\dfrac{100}{3}\)

Tách ra đi bạn ơi, dài quá

a: \(=\dfrac{x^3+2x+2x-2-x^2-x-1}{\left(x-1\right)\left(x^2+x+1\right)}\)

\(=\dfrac{x^3-x^2+3x-3}{\left(x-1\right)\left(x^2+x+1\right)}=\dfrac{x^2+3}{x^2+x+1}\)

b: \(=\dfrac{x^2-2x-3+x^2+2x-3+2x-2x^2}{\left(x-3\right)\left(x+3\right)}\)

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

c: \(=\dfrac{6-7+x}{3\left(x-1\right)}=\dfrac{x-1}{3\left(x-1\right)}=\dfrac{1}{3}\)

d: \(=\dfrac{x^3+2x+2x-2-x^2-x-1}{\left(x-1\right)\left(x^2+x+1\right)}=\dfrac{x^3-x^2+3x-3}{\left(x-1\right)\left(x^2+x+1\right)}=\dfrac{x^2+3}{x^2+x+1}\)