Question

Tìm x thuộc Z biết

a ) \(\frac{x-1}{9}\)= \(\frac{8}{3}\)

b ) \(\frac{-x}{4}\)=\(\frac{-9}{x}\)

c ) \(\frac{x}{4}\)= \(\frac{18}{x+1}\)

Answer 1

a, \(\frac{x-1}{9}=\frac{8}{3}\)

\(\Rightarrow\left(x-1\right).3=8.9\)

\(\Rightarrow\left(x-1\right).3=72\)

\(\Rightarrow x-1=72:3\)

\(\Rightarrow x-1=24\)

\(\Rightarrow x=24+1\)

\(\Rightarrow x=25\)

b, \(\frac{-x}{4}=\frac{-9}{x}\)

\(\Rightarrow-x.x=-9.4\)

\(\Rightarrow-\left(x^2\right)=-36\)

\(\Rightarrow x^2=36\)

\(\Rightarrow\orbr{\begin{cases}x=6\\x=-6\end{cases}}\)

c, \(\frac{x}{4}=\frac{18}{x+1}\)

\(\Rightarrow x\left(x+1\right)=4.18\)

\(\Rightarrow x.x+x.1=72\)

\(\Rightarrow x^2+x=72\)

\(\Rightarrow x^2+x-72=0\)

\(\Rightarrow x^2+x-8^2+8=0\)

\(\Rightarrow x=8\)

Answer 2

a) x-1=24

=>x=24+1=25

=> x=25

b)=>-(x^2)=-36

=>x=6

k mik nha

Answer 3

a) \(\frac{x-1}{9}=\frac{8}{3}\)

\(\Leftrightarrow3\left(x-1\right)=9\cdot8\)

\(\Leftrightarrow3x-3=72\)

\(\Leftrightarrow3x=75\)

\(\Leftrightarrow x=25\)

Answer 4

\(a,\frac{x-1}{9}=\frac{8}{3}\)

\(=>\left(x-1\right).3=8.9=72\)

\(=>x-1=72:3=24\)

\(=>x=25\)

\(b,\frac{-x}{4}=\frac{-9}{x}\)

\(=>\frac{x}{-4}=\frac{-9}{x}\)

\(=>x^2=\left(-9\right).\left(-4\right)=36\)

\(=>x^2=36=6^2\)

\(=>x=6\)

\(c,\frac{x}{4}=\frac{18}{x+1}\)

\(=>x^2+x=72\)

\(=>x^2+x-8^2-8=0\)

\(=>x=8\)

Answer 5

a, \(\frac{x-1}{9}=\frac{8}{3}\Leftrightarrow3x-3=72\Leftrightarrow3x=75\Leftrightarrow x=25\)

b, \(\frac{-x}{4}=\frac{-9}{x}\Leftrightarrow-x^2=-36\Leftrightarrow x^2=36\Leftrightarrow x=\pm6\)

c, \(\frac{x}{4}=\frac{18}{x+1}\Leftrightarrow x^2+x=72\)

\(\Leftrightarrow x^2+x-72=0\Leftrightarrow\left(x-8\right)\left(x+9\right)=0\Leftrightarrow\orbr{\begin{cases}x=8\\x=-9\end{cases}}\)