Răspuns:
Explicație pas cu pas:
19
b(a/b+5)/b(4a/b+1)=7/4 notam a/b=u
(u+5)/(4u+1)=7/4 4(u+5)=7(4u+1) 4u+20=7u+7 13=3u
a/b=13/3
20
y(3x/y+1)/y(x/y+2)=4/5 (3s+1)/(s+2)=4/5 4(s+2)=5(3s+1)
4s+8=15s+5 3=11s s=3/11
x/y=3/11
21
y(3x/y+4)/y(2x/y+1)=8/3 (3t+4)/(2t+1)=8/3
3(3t+1)=8(2t+1) 9t+3=16t+8 -5=7t t=-5/7
x/y=-5/7
