\(3x\left(x+4\right)-3x^2-4=0\\ \Rightarrow3x^2+12x-3x^2-4=0\\ \Rightarrow12x-4=0\\ \Rightarrow12x=4\\ \Rightarrow x=\dfrac{1}{3}\)

\(3^x.3^2.3=243.3\\ \Rightarrow3^x.3^2=243\\ \Rightarrow3^x.3^2=3^5\\ \Rightarrow3^x=3^5:3^2\\ \Rightarrow3^x=3^3\\ \Rightarrow x=3\)

=>3^x*3^3=3^5*3

=>x+3=6

=>x=3

\(3x^2y^3-x^2y-M=x^2y^3+x^2y\\ \Rightarrow M=3x^2y^3-x^2y-x^2y^3-x^2y\\ \Rightarrow M=2x^2y^3-2x^2y\)

\(\Leftrightarrow M=3x^2y^3-x^2y-x^2y^3-x^2y=2x^2y^3-2x^2y\)

ai cũng lười vào fx để gõ phân số

Đặt \(\frac{x}{2}=\frac{y}{3}=\frac{z}{5}=k\Rightarrow x=2k;y=3k;z=5k\)

thay x=2k;y=3k;z=5k vào x.y.z=810 ta được:

2k.3k.5k=810

30.k³=810

k³=27

=>k=3

=>x=2.3=6

y=3.3=9

z=5.3=15

Ta đặt \(\frac{x}{2}=\frac{y}{3}=\frac{z}{5}=k\)

\(\vec{ }\)

x =2k; y= 3k; z= 5k

ta có: 

2k. 3k.5k= 810

30.k³=810

k³     =810 :30

k³= 27

=>k=3

=>x=2.3=6

y=3.3=9

z=5.3=15

Vậy: x= 6; y=9; y=15

a) 3x = 2y \(\Rightarrow\)\(\frac{x}{2}=\frac{y}{3}\)\(\Rightarrow\frac{x}{2}.\frac{1}{5}=\frac{y}{3}.\frac{1}{5}\)\(\Rightarrow\frac{x}{10}=\frac{y}{15}\)

\(7y=5z\Rightarrow\frac{y}{5}=\frac{z}{7}\Rightarrow\frac{y}{5}.\frac{1}{3}=\frac{z}{7}.\frac{1}{3}\Rightarrow\frac{y}{15}=\frac{z}{15}\)

\(\Rightarrow\frac{x}{10}=\frac{y}{15}=\frac{z}{21}\Rightarrow\frac{x+y+z}{10+15+21}=\frac{32}{46}=\frac{2}{3}\)

\(\hept{\begin{cases}x=10.\frac{2}{3}=\frac{20}{3}\\y=15.\frac{2}{3}=10\\z=21.\frac{2}{3}=14\end{cases}}\)

Vậy \(\hept{\begin{cases}x=10.\frac{2}{3}=\frac{20}{3}\\y=15.\frac{2}{3}=10\\z=21.\frac{2}{3}=14\end{cases}}\)