[tex]a)\\\\P = 2 (ab + bc + ac)\\\\P = 2 ab+2bc+2ac\\\\ 2ab +2ac=P-2bc\\\\a(2b+2c)=P-2b\ \ |:(2b+2c)\\\\a=\frac{P-2b}{2b+2c} =\frac{P-2b}{2(b+ c)}[/tex]
[tex]b)\\\\ P = 2 ab+2bc+2ac\\\\ 2ab +2bc=P-2ac\\\\b(2a+2c)=P -2c\ \ |:(2a+2c)\\\\b=\frac{ P-2ac}{2a+2c} =\frac{P -2ac}{2(a+ c)}[/tex]
[tex]c)\\\\ P = 2 ab+2bc+2ac\\\\ 2ac +2 bc =P-2ab\\\\c( 2a+2b)=P -2ab\ \ |:(2a+2b)\\\\b=\frac{ P-2ab}{2a+2b} =\frac{P -2ab}{2(a+ b)}[/tex]