Question

1, Cho 2x;3y tỉ lệ nghịch với 3,4;x và z tỉ lệ thuận với 4,5; x-2y+3z=1. Tính x-y-z

2. Tìm x: \(\left(2x-3\right)^2\)-\(2\left(3x+1\right)^2\)=\(2x\left(x-2\right)+\left(x-1\right)\left(x+2\right)\)

 

 

Answer 1

1

2x . 3=3y .4

=> x=2y=>\(\frac{x}{2}=y\Rightarrow\frac{x}{4}=\frac{y}{2}\)

\(\frac{x}{4}=\frac{z}{5}\)

\(\Rightarrow\frac{x}{4}=\frac{y}{2}=\frac{z}{5}=\frac{x-2y+3z}{4-4+15}=\frac{1}{15}=\)

x=1/15x4=4/15

y=1/15x2=2/15

z=1/15x6=1/10

\(\Rightarrow x-y-z=\frac{4}{15}-\frac{2}{15}-\frac{1}{10}=\frac{1}{30}\)

 

Answer 2

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

4\(x^2\)-12x+9-2(9\(x^2\)+6x+1)=2\(x^2\)-4x+\(x^2\)+2x-x-2

4\(x^2\)-12x+9-18\(x^2\)-12x-2=2\(x^2\)-4x+\(x^2\)+2x-x-2

(4\(x^2\)-18\(x^2\)-2\(x^2\)-\(x^2\)) +(-12x-12x+4x-2x+x)+(9-2+2)=0

-17\(x^2\)-21x+9=0