\(a,\left(-\dfrac{13}{7}-\dfrac{4}{9}\right)-\left(-\dfrac{10}{7}-\dfrac{4}{9}\right)\\ =-\dfrac{13}{7}-\dfrac{4}{9}+\dfrac{10}{7}+\dfrac{4}{9}\\ =-\dfrac{3}{7}.\)

\(126.44+126.57-126+300\\ =126.\left(44+57-1\right)+300\\ =126.100+300\\ =12600+300\\ =12900.\)

\(\dfrac{2}{5}-x=2-\dfrac{3}{4}\\ \Rightarrow\dfrac{2}{5}-x=\dfrac{5}{4}\\ \Rightarrow x=-\dfrac{17}{20}.\)

C. answer

\(a,\dfrac{3}{7}=\dfrac{2x+1}{3x+5}\\\Rightarrow3x+15=14x+7\\ \Rightarrow3x-14x=7-15 \\ \Rightarrow-11x=-8\\ \Rightarrow x=\dfrac{8}{11}.\\ b,\dfrac{x+1}{x-2}=\dfrac{3}{4}\\ \Rightarrow4x+4=3x-6\\ \Rightarrow4x-3x=-6-4\\ \Rightarrow x=-10.\\ c,\dfrac{2x+3}{7}=\dfrac{4x-1}{15}\\ \Rightarrow30x+45=28x-7\\\Rightarrow30x-28x=-7-45\\ \Rightarrow2x=-52\\ \Rightarrow x=-26.\)

\(d,\dfrac{6x-5}{-7}=\dfrac{5x-3}{-5}\\ \Rightarrow-30x+25=-35x+21\\ \Rightarrow-30x+35x=21-25\\ \Rightarrow5x=-4\\ \Rightarrow x=-\dfrac{4}{5}.\)

Sửa lỗi: improves

You know, we have many kinds of game that we can play them anytime.But in my class, we find chess the most exciting.Because it improve our brain.

Of course, i think i want to play a game for fun. Because it helps me to relax and good for my happiness.

=> What is your favourite food?

Sửa bài:

   Đặt biểu thức là A. ta được:

     \(\dfrac{A}{5}=\dfrac{5}{1.6}+\dfrac{5}{6.11}+...+\dfrac{5}{26.31}\\ \dfrac{A}{5}=1-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{11}+...+\dfrac{1}{26}-\dfrac{1}{31}\\ \dfrac{A}{5}=\dfrac{30}{31}\\ A=\dfrac{150}{31}.\)