Ta có:5x11=55;4x13=52 

Do 55>52

=>\(\dfrac{5}{13}>\dfrac{4}{11}\)

Ta có:\(\dfrac{1}{4}=\dfrac{1\times5}{4\times5}=\dfrac{5}{20};\dfrac{2}{5}=\dfrac{2\times4}{5\times4}=\dfrac{8}{20}\)

=> các phân số cần tìm là \(\dfrac{6}{20}=\dfrac{3}{10};\dfrac{7}{20}\)

<=>\(\dfrac{x+1}{124}+\dfrac{x+2}{123}-\dfrac{x+3}{122}-\dfrac{x+4}{121}=0\)

<=>\(\left(\dfrac{x+1}{124}+1\right)+\left(\dfrac{x+2}{123}+1\right)-\left(\dfrac{x+3}{122}+1\right)-\left(\dfrac{x+4}{121}+1\right)=0\)

<=>\(\dfrac{x+125}{124}+\dfrac{x+125}{123}-\dfrac{x+125}{122}-\dfrac{x+125}{121}=0\)

<=>\(\left(x+125\right)\left(\dfrac{1}{124}+\dfrac{1}{123}-\dfrac{1}{122}-\dfrac{1}{121}\right)=0\)

<=>x+125=0

<=>x=-125

Mình viết phần thân thôi nha

n khai báo là interger

n:=0;

While n<>100 do

 Begin

 Write(n,' ');

 inc(n);

 end;

\(4x^3-4x^2-x+1=0\)

<=>\(\left(2x+1\right)\left(x-1\right)\left(2x-1\right)=0\)

<=>\(\left[{}\begin{matrix}x=\dfrac{-1}{2}\\x=1\\x=\dfrac{1}{2}\end{matrix}\right.\)

vì 10x12=120; 11x11=121

=>\(\dfrac{10}{11}< \dfrac{11}{12}\)

1.D

2.A

3.C

4.A

Chữ Tham khảo âu :>

\(\dfrac{1}{8};\dfrac{2}{7};\dfrac{3}{6};\dfrac{4}{5}\)