\(5x^2-16x+3=5x^2-15x-x+3=5x\left(x-3\right)-\left(x-3\right)=\left(5x-1\right)\left(x-3\right)\)

cho a,b,c>0 và \(a+b+c\le1\)

cmr \(\dfrac{1}{a^2+2bc}+\dfrac{1}{b^2+2ac}+\dfrac{1}{c^2+2ab}\ge9\)

đúng đề ko bạn

2x+5=4(x-1)-2(x-3)

\(\Leftrightarrow2x+5=4x-4-2x+6\)

\(\Leftrightarrow2x-4x+2x=-4+6-5\)

\(\Leftrightarrow0x=3\)(vô lí)

\(\Rightarrow\)Phương trình vô nghiệm

b) 2x-3=2(x-3)

\(\Leftrightarrow2x-3=2x-6\)

\(\Leftrightarrow2x-2x=-6+3\)

\(\Leftrightarrow0x=-3\)( vô lí)

Vậy phương trình vô nghiệm

\(\dfrac{87552}{35}\)

đề bài bạn

\(\dfrac{x}{y}=\dfrac{9}{7}\Rightarrow\dfrac{x}{9}=\dfrac{y}{7}\)

\(\dfrac{y}{z}=\dfrac{7}{3}\Rightarrow\dfrac{y}{7}=\dfrac{z}{3}\)

\(\Rightarrow\dfrac{x}{9}=\dfrac{y}{7}=\dfrac{z}{3}\)

AD TC DTSBN ta có 

\(\dfrac{x}{9}=\dfrac{y}{7}=\dfrac{z}{3}=\dfrac{x-y+z}{9-7+3}=\dfrac{-15}{5}=-3\)

\(\Rightarrow\dfrac{x}{9}=-3\Rightarrow x=-27\)

\(\dfrac{y}{7}=-3\Rightarrow y=-21\)

\(\dfrac{z}{3}=-3\Rightarrow z=-9\)