a: 10x-30=0
=>10x=30
hay x=3
b: 3x+x+16=0
=>4x+16=0
hay x=-4
c: x-5=7-x
=>2x=12
hay x=6
d: \(\left(7-3x\right)\left(9+x\right)=0\)
=>7-3x=0 hoặc x+9=0
=>x=7/3 hoặc x=-9
d. \(\Leftrightarrow\left[{}\begin{matrix}7-3x=0\\9+x=0\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{7}{3}\\x=-9\end{matrix}\right.\)
e. \(ĐK:x\ne-1;-5\)
\(\dfrac{x-5}{x+1}=\dfrac{x-4}{x+5}\)
\(\Leftrightarrow\dfrac{\left(x-5\right)\left(x+5\right)}{\left(x+1\right)\left(x+5\right)}=\dfrac{\left(x-4\right)\left(x+1\right)}{\left(x+1\right)\left(x+5\right)}\)
\(\Leftrightarrow\left(x-5\right)\left(x+5\right)=\left(x-4\right)\left(x+1\right)\)
\(\Leftrightarrow x^2-25=x^2+x-4x-4\)
\(\Leftrightarrow3x=21\)
\(\Leftrightarrow x=7\left(tm\right)\)
