Question

Tìm x biết:

a) \(\frac{x-3}{x+5}\)=\(\frac{5}{7}\)

b)\(\frac{7}{x-1}\)=\(\frac{x+1}{9}\)

c)\(\frac{x+4}{20}\)=\(\frac{5}{x+4}\)

d)\(\frac{x-1}{x+2}\)=\(\frac{x-2}{x+3}\)

e)\(\frac{x}{4}\):2=4:\(\frac{x}{2}\)

Answer 1

a) \(\frac{x-3}{x+5}=\frac{5}{7}\)

\(\Rightarrow\left(x-3\right).7=\left(x+5\right).5\)

\(\Rightarrow7x-21=5x+25\)

\(\Rightarrow7x-5x=21+25\)

\(\Rightarrow2x=46\)

\(\Rightarrow x=23\)

Vậy \(x=23\)

Answer 2

b) \(\frac{7}{x-1}=\frac{x+1}{9}\)

\(\Rightarrow\left(x-1\right).\left(x+1\right)=7.9\)

\(\Rightarrow\left(x-1\right)x-\left(x+1\right)=7.9\)

\(\Rightarrow x^2-x-x-1=63\)

\(\Rightarrow x^2-1=63\)

\(\Rightarrow x^2=64\)

\(\Rightarrow x=8\) hoặc \(x=-8\)

Vậy \(x=8\) hoặc \(x=-8\)

c) \(\frac{x+4}{20}=\frac{5}{x+4}\)

\(\Rightarrow\left(x+4\right)^2=100\)

\(\Rightarrow x+4=\pm10\)

+) \(x+4=10\Rightarrow x=6\)

+) \(x+4=-10\Rightarrow x=-16\)

Vậy \(x\in\left\{6;-16\right\}\)

 

Answer 3

e) \(\frac{x}{4}:2=4:\frac{x}{2}\)

\(\Rightarrow\frac{x}{4}.\frac{1}{2}=4.\frac{2}{x}\)

\(\Rightarrow\frac{x}{8}=\frac{8}{x}\)

\(\Rightarrow x^2=64\)

\(\Rightarrow x=\pm8\)

Vậy \(x=\pm8\)

Answer 4

a)x=22

 

Answer 5

e)x=1

Answer 6

nhầm nha

phải là 

a)x=22

b)x=8