1. (a(b+c))/(b^2+c^2))
b=2/3*a
c=7/4(a+b)=7/4(3/3*a+2/3*a)=35/12*a
a(b+c)=a(2/3*a+35/12*a)=a^2*43/12
b^2+c^2=4/9*a^2+1225/144*a^2=a^2*1289/144
raportul va fi: (a^2*43/12)*(144/a^2*1289)=516/1289
2. x/y=75/100=3/4 =>x=3y/4
5y-7x=20y/4-21y/4=-y/4
6y-8x=24y/4-24y/4=0
fractia nu are sens deoarece nu exista impartirea la 0
3. (10a+b)/(10b+a)=4/7
70a+7b=40b+4a
66a=33b
b=2a
a=1 b=2 ab=12
a=2 b=4 ab=24
a=3 b=6 ab=36
a=4 b=8 ab=48