Question

[V]

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

[Lê Anh Tú]

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

[Ngô Lan Chi]

a) x-1=24

=>x=24+1=25

=> x=25

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

=>x=6

k mik nha