Phép cộng phân số (tiếp theo)

\(2:x-\dfrac{1}{3}=\dfrac{2}{5}\\ 2:x=\dfrac{2}{5}+\dfrac{1}{3}\\ 2:x=\dfrac{11}{15}\\ x=2:\dfrac{11}{15}\\ x=\dfrac{30}{11}\)

`2:x-1/3=2/5`

`=>2:x=2/5+1/3`

`=>2:x=6/15+5/15`

`=>2:x=11/15`

`=>x=2:11/15`

`=>x=2xx15/11`

`=>x=30/11`

Vậy `x=30/11` 

`#`𝐷𝑎𝑖𝑙𝑧𝑖𝑒𝑙

=2*4/5*3/4=2*3/5=6/5

`(4242×12×15)/(2121×15×20)`

`= (2xx2121×12×15)/(2121×15×20)`

`=(2×12)/20`

`= 24/20 = 6/5`

\(\dfrac{4242\times12\times15}{2121\times15\times20}=\dfrac{2121\times2\times4\times3\times15}{2121\times15\times4\times5}\\ =\dfrac{2\times3}{5}=\dfrac{6}{5}\)

`(64×15×9)/(72×45×6) `

`=(8xx8×3xx5×9)/(8xx9×5xx9×2xx3) `

`=8/(9×2) `

`= 4/9`

\(\dfrac{1}{3}+\dfrac{1}{6}+\dfrac{4}{3}+\dfrac{2}{6}+\dfrac{2}{3}+\dfrac{5}{6}\)

\(=\left(\dfrac{1}{3}+\dfrac{4}{3}+\dfrac{2}{3}\right)+\left(\dfrac{1}{6}+\dfrac{2}{6}+\dfrac{5}{6}\right)\)

\(=\dfrac{7}{3}+\dfrac{8}{6}\)\(=\dfrac{7}{3}+\dfrac{4}{3}\)

\(=\dfrac{11}{3}\)

`4/5+3/7`

`=(4xx7)/(5xx7)+(3xx5)/(7xx5)`

`=(28)/(35)+(15)/(35)`

`=(28+15)/(35)`

`=(43)/(35)`

\(=\dfrac{4.7+3.5}{35}=\dfrac{43}{35}\)

= 43/35

`1/25 + 7/3 + 4/25`

`=(1/25 + 4/25) + 7/3`

`=5/25 + 7/3`

`=1/5 + 7/3`

`=3/15 + 35/15`

`=(35+3)/15`

`=38/15`

\(\dfrac{1}{25}+\dfrac{7}{3}+\dfrac{4}{25}\)

\(=\left(\dfrac{1}{25}+\dfrac{4}{25}\right)+\dfrac{7}{3}\)

\(=\dfrac{1}{5}+\dfrac{7}{3}\)

\(=\dfrac{3}{15}+\dfrac{35}{15}\)

\(=\dfrac{3+35}{15}=\dfrac{38}{15}\)

\(\dfrac{1}{25}+\dfrac{7}{3}+\dfrac{4}{25}=\) 

\(=\left(\dfrac{1}{25}+\dfrac{4}{25}\right)+\dfrac{7}{3}\) 

\(=\dfrac{5}{25}+\dfrac{7}{3}\) 

\(=\dfrac{1}{5}+\dfrac{7}{3}\) 

\(=\dfrac{3}{15}+\dfrac{35}{15}\) 

\(=\dfrac{38}{15}\)

7/3

\(\dfrac{2}{1}+\dfrac{1}{3}=2+\dfrac{1}{3}=2\dfrac{1}{3}\)

`2/1 + 1/3 = (2xx3)/(1xx3) + 1/3 = 6/3 + 1/3 = 7/3`

=>(x-2)²=81

=>x-2=9 hoặc x-2=-9

=>x=11 hoặc x=-7

\(\dfrac{-3}{x-2}=\dfrac{x-2}{-27}\\ \Leftrightarrow\left(x-2\right)^2=\left(-3\right)\cdot\left(-27\right)\\ \Leftrightarrow\left(x-2\right)^2=81\\ \Leftrightarrow\left(x-2\right)^2=\left(\pm9\right)^2\\ \Leftrightarrow\left[{}\begin{matrix}x-2=9\\x-2=-9\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=11\\x=-7\end{matrix}\right.\)

\(\dfrac{-3}{x-2}=\dfrac{x-2}{-27}\)

`=> (x-2)  xx (x-2) = -3 xx (-27)`

` (x-2)^2 = 81`

\(\Leftrightarrow\left[{}\begin{matrix}x-2=9\\x-2=-9\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=11\\x=-7\end{matrix}\right.\)

17/20=1/4+1/5+1/2,5

ChọnC

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