Răspuns:
Explicație pas cu pas:
[tex]\dfrac{a}{b}=\dfrac{1}{2},~~ deci~~a*2=b*1,~~deci~b=2a.\\C=\dfrac{5a-2b}{5a+2b}*\dfrac{3a-b}{7a+b}=\dfrac{5a-2*2a}{5a+2*2a} *\dfrac{3a-2a}{7a+2a}=\dfrac{a}{9a}*\dfrac{a}{9a}=\dfrac{1}{9}*\dfrac{1}{9}=\dfrac{1}{81}[/tex]