21:x+3=x:3+9
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26 tháng 7 2023
a: \(=\dfrac{3}{5}:\dfrac{7}{5}=\dfrac{3}{5}\cdot\dfrac{5}{7}=\dfrac{3}{7}\)
b: \(=\dfrac{9}{17}\left(\dfrac{8}{5}-\dfrac{3}{5}\right)+\dfrac{8}{17}\)
=9/17+8/17=1
c: =>x-3/10=7/15*1/5=7/75
=>x=7/75+3/10=59/150
27 tháng 1 2023
\(a.\dfrac{6}{5}=\dfrac{18}{x}\Rightarrow x=\dfrac{18\cdot5}{6}=15\\ \text{Vậy}\text{ }x=15.\)
\(b.\dfrac{3}{4}=\dfrac{-21}{x}\Rightarrow x=\dfrac{-21\cdot4}{3}=28\\ \text{ }\text{ }\text{ }\text{ }\text{Vậy }x=28.\)
\(c.\dfrac{x}{4}=\dfrac{21}{28}\Rightarrow x=\dfrac{21\cdot4}{28}=3\\ \text{Vậy }x=3.\)
\(d.\dfrac{-8}{2x}=\dfrac{3}{-9}\Rightarrow x=\dfrac{-8\cdot\left(-9\right)}{3}:2=12\\ \text{Vậy }x=12.\)
\(e.\dfrac{-4}{11}=\dfrac{x}{22}=\dfrac{40}{z}\\ \Rightarrow x=\dfrac{-4\cdot22}{11}=-8\\ \Rightarrow z=\dfrac{22\cdot40}{-8}=-110\\ \text{Vậy }x=-8;z=-110.\)
\(f.\dfrac{-3}{4}=\dfrac{x}{20}=\dfrac{21}{y}\\ \Rightarrow x=\dfrac{-3\cdot20}{4}=-15\\ \Rightarrow y=\dfrac{21\cdot20}{-15}=-28\\ \text{Vậy }x=-15;y=-28.\)
\(g.\dfrac{-4}{8}=\dfrac{x}{-10}=\dfrac{-7}{y}=\dfrac{z}{-24}\\ \Rightarrow x=\dfrac{-4\cdot\left(-10\right)}{8}=5\\ \Rightarrow y=\dfrac{-7\cdot\left(-10\right)}{5}=14\\ \Rightarrow z=\dfrac{-7\cdot\left(-24\right)}{14}=12\\ \text{Vậy }x=5;y=14;z=12.\)
\(h.\dfrac{x}{4}=\dfrac{9}{x}\\ \Rightarrow x\cdot x=9\cdot4\\ \Rightarrow x\cdot x=36\\ \Rightarrow x\cdot x=6\cdot6\\ \text{Vậy }\text{cả hai }x=6.\)
30 tháng 12 2021
\(=\dfrac{5x+15+4x-12-x+21}{\left(x-3\right)\left(x+3\right)}=\dfrac{8x+24}{\left(x-3\right)\left(x+3\right)}=\dfrac{8}{x-3}\)
KV
7 tháng 8 2023
(x - 2)³ - (x - 9)³ = 21(x - 8)²
x³ - 6x² + 12x - 8 - x³ + 27x² - 243x + 729 = 21x² - 336x + 1344
-6x² + 27x² + 12x - 243x - 8 + 729 -21x² + 336x - 1344 = 0
105x - 623 = 0
105x = 623
x = 89/15
7 tháng 8 2023
(x-2)^3-(x-9)^3=21(x-8)^2
=>x^3-6x^2+12x-8-x^3+27x^2-243x+729=21(x^2-16x+64)
=>-231x+721=-336x+1344
=>105x=1344-721=623
=>x=623/105=89/15
6 tháng 2 2021
Ta có: \(B=\left(\dfrac{21}{x^2-9}-\dfrac{x-4}{3-x}-\dfrac{x-1}{3+x}\right):\left(1-\dfrac{1}{x+3}\right)\)
\(=\left(\dfrac{21}{\left(x-3\right)\left(x+3\right)}+\dfrac{\left(x-4\right)\left(x+3\right)}{\left(x-3\right)\left(x+3\right)}-\dfrac{\left(x-1\right)\left(x-3\right)}{\left(x+3\right)\left(x-3\right)}\right):\left(\dfrac{x+3}{x+3}-\dfrac{1}{x+3}\right)\)
\(=\dfrac{21+x^2+3x-4x-12-\left(x^2-4x+3\right)}{\left(x+3\right)\left(x-3\right)}:\dfrac{x+3-1}{x+3}\)
\(=\dfrac{x^2-x+9-x^2+4x-3}{\left(x+3\right)\left(x-3\right)}:\dfrac{x+2}{x+3}\)
\(=\dfrac{3x+6}{\left(x+3\right)\left(x-3\right)}:\dfrac{x+2}{x+3}\)
\(=\dfrac{3\left(x+2\right)}{\left(x+3\right)\left(x-3\right)}\cdot\dfrac{x+3}{x+2}\)
\(=\dfrac{3}{x-3}\)
TL
5
21:x+3=x:3+9
<=>\(\frac{21}{x}+3=\frac{x}{3}+9\)
ĐKXĐ:x khác 0
=>63+9x=x2+27x
<=>x2+27x-9x-63=0
<=>x2-18x-63=0
<=>x2-21x+3x-63=0
<=>x(x-21)+3(x-3)=0
<=>(x-21)(x+3)=0
<=>x-21=0 hoặc x+3=0
<=>x=21 hoặc x=-3
Vậy x={-3;21}