[tex]\displaystyle\bf\\yc^{2} -yb^{2} =y\cdot(c^{2} -b^{2} )=y\cdot(c-b)\cdot(c+b)\\\\\\y=\frac{1}{4} \ \ \ ; \ \ \ c=4,29 \ \ \ ; \ \ \ b=0,29\\\\\\y\cdot(c-b)\cdot(c+b)=\frac{1}{4} \cdot(4,29-0,29)\cdot(4,29+0,29)=\\\\\\=\frac{1}{4} \cdot 4\cdot4,58=1\cdot 4,58=4,58\\\\\\Otvet: \ 4,58[/tex]