Có:

\(\frac{x}{3}=\frac{y}{8}=\frac{z}{5}=\frac{3x}{9}=\frac{2z}{10}\)

Áp dụng tính chất của dãy tỉ số bằng nhau, ta có:

\(\frac{x}{3}=\frac{y}{8}=\frac{z}{5}=\frac{3x}{9}=\frac{2z}{10}=\frac{3x+y-2z}{9+8-10}=\frac{14}{7}=2\)

\(\frac{x}{3}=2\Rightarrow x=6\)

\(\frac{y}{8}=2\Rightarrow y=16\)

\(\frac{z}{5}=2\Rightarrow z=10\)

a) 10(1-y)-8y(y-1)

= 10(1-y) + 8y(1-y)

= (1-y)(10+8y)

b) 2y + 3z + 6y +y

= 9y+3z

= 3( 3y+z)

a) \(4x^2-49=0\)

<=> \(\left(2x-7\right)\left(2x+7\right)=0\)

<=> \(\left\{{}\begin{matrix}2x-7=0\\2x+7=0\end{matrix}\right.\)

<=> \(\left\{{}\begin{matrix}x=\frac{7}{2}\\x=-\frac{7}{2}\end{matrix}\right.\)

b) x² + 36 = 12x

<=>x² + 36 - 12x=0

<=> (x-6)²=0

<=> x-6 =0

<=> x=6