\(\left(\dfrac{21}{4}+\dfrac{-7}{2}\right)+\dfrac{43}{16}-\dfrac{11}{16}+\dfrac{-3}{12}-\dfrac{-7}{2}\\ =\left(\dfrac{21}{4}+\dfrac{-7}{2}\right)+\dfrac{43}{16}-\dfrac{11}{16}+\dfrac{-3}{12}-\dfrac{-7}{2}\\ =\left(\dfrac{63}{12}+\dfrac{-3}{12}\right)+\left(\dfrac{-7}{2}-\dfrac{-7}{2}\right)+\left(\dfrac{43}{16}-\dfrac{11}{16}\right)\\ =5+0+2\\ =7\)

\(a,\dfrac{x}{8}=\dfrac{7}{-2}\\ \Rightarrow x=-28\\ b,\dfrac{1-2x}{6}=\dfrac{-1}{2}\\ \Leftrightarrow2-4x=-6\\ \Leftrightarrow4x=8\\ \Leftrightarrow x=2\\ c,\dfrac{x+2}{3}=\dfrac{x+3}{4}\\ \Leftrightarrow4x+8=3x+9\\ \Leftrightarrow x=1\\ d,\dfrac{10}{2-x}=2\\ \Leftrightarrow4-2x=10\\ \Leftrightarrow2x=-6\\ \Leftrightarrow x=-3\)

Chu vi hình bình hành là:

`(3/5+2)xx2=26/5(m)`

Đáp số:`26/5m`

\(y-\dfrac{2}{3}=\dfrac{4}{5}\times\dfrac{3}{4}\\ y-\dfrac{2}{3}=\dfrac{3}{5}\\ y=\dfrac{3}{5}+\dfrac{2}{3}\\ y=\dfrac{9}{15}+\dfrac{10}{15}\\ y=\dfrac{19}{15}\)

\(\dfrac{2-x}{-4}=\dfrac{-9}{2-x}\\ \Leftrightarrow\left(2-x\right)^2=36\\ \Leftrightarrow\left[{}\begin{matrix}2-x=6\\2-x=-6\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=-4\\x=8\end{matrix}\right.\)

Thế còn đây :>

nó là con Mai lợn đấy

`13,25+13,25:0,2+13,25:0,25`

`=13,25+13,25xx5+13,25xx4`

`=13,25xx(1+5+4)`

`=13,25xx10`

`=132,5`

Thời gian ô tô đi từ A đến B là:

9h-6h30'=2h30'=2,5h

Vận tốc của ô tô là:
130:2,5=52(km/h)

Đáp số: 52km/h

`3/7xx14/5+32/5xx3/7+3/7xx9/5`

`=3/7xx(14/5+32/5+9/5)`

`=3/7xx55/5`

`=3/7xx5`

`=15/7`