a) a+b=56
a=3/4xb=3b/4
3b/4+b=56 aducem la acelasi numitor
(3b+4b)/4=56
7b=56x4
b=224/7
b=32
a=56-b
a=56-32
a=24
deci 24+32=56
b) 8,(2)=(82-8)/9=74/9
b-a=74/9
a=b/3
b-b/3=74/9
(3b-b)/3=74/9
2b/3=74/9
2bx9=74x3
18b=222
b=222/18=simplif.cu 2=111/9
b=111/9
a=b/3=111/9:3=111/(9x3)=111/27= simplif.cu 3=37/9
a=37/9
deci
111/9-37/9=74/9