Răspuns:
21.x/y=7/4
22.x/y=2/9
Explicație pas cu pas:
21. 3x+4y/2x+y=8/3 => 3(3x+4y)=8(2x+y)
=>9x+12y=16x+8y
=>-7x=-4y×(-1)
=>7x=4y=>x/y=7/4
22. 7x+3y/4x+5y=3/2=> 2(7x+3y)=3(4x+5y)
=>14x+6y=12x+15y =>2x=9y => x/y=2/9
9x+12y=16x+8y ; 12y-8y=16x-9x ; 4y=7x ; x/y=4/7 ; 22) 14x+6y= 12x+15 y ; 14x-12x=15y-6y ; 2x=9y ; x/y=9/2
