Violympic toán 8

HH

1. giải phương trình

a, \(\frac{7x-3}{x-1}=\frac{2}{3}\)

b, \(\frac{2\left(3-7x\right)}{1+x}=\frac{1}{2}\)

c,\(\frac{5x-1}{3x+2}=\frac{5x-7}{3x-1}\)

d,\(\frac{4x+7}{x-1}=\frac{12x+5}{3x+4}\)

NT
18 tháng 4 2020 lúc 19:16

a) ĐKXĐ: \(x\ne1\)

Ta có: \(\frac{7x-3}{x-1}=\frac{2}{3}\)

\(\Leftrightarrow3\left(7x-3\right)=2\left(x-1\right)\)

\(\Leftrightarrow21x-9=2x-2\)

\(\Leftrightarrow21x-9-2x+2=0\)

\(\Leftrightarrow19x-7=0\)

\(\Leftrightarrow19x=7\)

hay \(x=\frac{7}{19}\)

Vậy: \(x=\frac{7}{19}\)

b) ĐKXĐ: \(x\ne-1\)

Ta có: \(\frac{2\left(3-7x\right)}{1+x}=\frac{1}{2}\)

\(\Leftrightarrow4\left(3-7x\right)=1+x\)

\(\Leftrightarrow12-28x-1-x=0\)

\(\Leftrightarrow11-29x=0\)

\(\Leftrightarrow29x=11\)

hay \(x=\frac{11}{29}\)

Vậy: \(x=\frac{11}{29}\)

c) ĐKXĐ: \(x\notin\left\{\frac{-2}{3};\frac{1}{3}\right\}\)

Ta có: \(\frac{5x-1}{3x+2}=\frac{5x-7}{3x-1}\)

\(\Leftrightarrow\left(5x-1\right)\left(3x-1\right)=\left(5x-7\right)\left(3x+2\right)\)

\(\Leftrightarrow15x^2-5x-3x+1=15x^2+10x-21x-14\)

\(\Leftrightarrow15x^2-8x+1=15x^2-11x-14\)

\(\Leftrightarrow15x^2-8x+1-15x^2+11x+14=0\)

\(\Leftrightarrow3x+15=0\)

\(\Leftrightarrow3x=-15\)

hay x=-5

Vậy: x=-5

d) ĐKXĐ: \(x\notin\left\{1;\frac{-4}{3}\right\}\)

Ta có: \(\frac{4x+7}{x-1}=\frac{12x+5}{3x+4}\)

\(\Leftrightarrow\left(4x+7\right)\left(3x+4\right)=\left(12x+5\right)\left(x-1\right)\)

\(\Leftrightarrow12x^2+16x+21x+28=12x^2-12x+5x-5\)

\(\Leftrightarrow12x^2+37x+28=12x^2-7x-5\)

\(\Leftrightarrow12x^2+37x+28-12x^2+7x+5=0\)

\(\Leftrightarrow44x+33=0\)

\(\Leftrightarrow44x=-33\)

hay \(x=\frac{-3}{4}\)

Vậy: \(x=\frac{-3}{4}\)

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H24
18 tháng 4 2020 lúc 19:19

Violympic toán 8

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H24
18 tháng 4 2020 lúc 19:24

Violympic toán 8

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HA
18 tháng 4 2020 lúc 19:29

a)

\(\frac{7x-3}{x-1}=\frac{2}{3}\\ \Leftrightarrow\frac{21x-9}{3\cdot\left(x-1\right)}-\frac{2x-2}{3\cdot\left(x-1\right)}=0\\ \Leftrightarrow\frac{21x-9-2x+2}{3\cdot\left(x-1\right)}=0\\ \Leftrightarrow\frac{19x-7}{3\cdot\left(x-1\right)}=0\\ \Rightarrow19x-7=0\\ \Rightarrow x=\frac{7}{19}\)

b)

\(\frac{2\cdot\left(3-7x\right)}{1+x}=\frac{1}{2}\\ \Leftrightarrow\frac{12-28x}{2\cdot\left(1+x\right)}-\frac{1+x}{2\cdot\left(1+x\right)}=0\\ \Leftrightarrow\frac{12-28x-1-x}{2\cdot\left(1+x\right)}=0\\ \Leftrightarrow\frac{11-29x}{2\cdot\left(1+x\right)}=0\\\Rightarrow11-29x=0\\ \Rightarrow x=\frac{11}{29}\)

c)

\(\frac{5x-1}{3x+2}=\frac{5x-7}{3x-1}\\ \Leftrightarrow\frac{15x^2-8x+1}{\left(3x+2\right)\cdot\left(3x-1\right)}-\frac{15x^2-11x-14}{\left(3x+2\right)\cdot\left(3x-1\right)}=0\\ \Leftrightarrow\frac{15x^2-8x+1-15x^2+11x+14}{\left(3x+2\right)\cdot\left(3x-1\right)}=0\\ \Leftrightarrow\frac{3x+15}{\left(3x+2\right)\cdot\left(3x-1\right)}=0\\ \Rightarrow3x+15=0\\ \Rightarrow x=-5\)

d)

\(\frac{4x+7}{x-1}=\frac{12x+5}{3x+4}\\ \Leftrightarrow\frac{12x^2+37x+28}{\left(x-1\right)\cdot\left(3x+4\right)}-\frac{12x^2-7x-5}{\left(x-1\right)\cdot\left(3x+4\right)}=0\\ \Leftrightarrow\frac{12x^2+37x+28-12x^2+7x+5}{\left(x-1\right)\cdot\left(3x+4\right)}=0\\ \Leftrightarrow\frac{44x+33}{\left(x-1\right)\cdot\left(3x+4\right)}=0\\ \Leftrightarrow44x+33=0\\ \Rightarrow x=-\frac{3}{4}\)

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