Question

Tìm x ; y ; z  biết rằng     x / 2 = 2y / 3 = 3z / 4 và x - y = 15

Answer 1

áp dụng t/c dãy tỉ số = nhau ta có:

\(\frac{x}{2}=\frac{2y}{3}=\frac{3z}{4}=\frac{x+2y+3z}{9}\)

x-y=15 => y=x-15

\(\frac{x}{2}=\frac{x+2y+3z}{9}\Leftrightarrow9x=2x+4y+6z\Leftrightarrow7x-4y=6z\Leftrightarrow7x-4\left(x-15\right)=6z\Leftrightarrow3x+60=6z\Leftrightarrow z=\frac{1}{2}x+10\)

\(\frac{2y}{3}=\frac{x+2y+3z}{9}\Leftrightarrow18y=3x+6y+9z\Leftrightarrow3x-12\left(x-15\right)+9\left(\frac{1}{2}x+10\right)=0\Leftrightarrow-\frac{9}{2}x=-270\Leftrightarrow x=60\)

=> y=60-15=45; z= \(\frac{1}{2}.60+10=40\)

Answer 2

vì x/2=2y/3 nen

x*3=2*2y=4y

3x=4y

x/4=y/3

theo tinh caht cua day ti so bang nhau ta co

x-y/4-3=15/1=15

Answer 3

ai đấy