[tex]a)\ P=2a\cdot2a-b\cdot b=\boxed{4a^{2}-b^{2}}\\\\dla \ a=0,5\ dm=5\ cm\ i \ b=3,4\ cm:\\\\P=4\cdot(5\ cm)^{2}-(3,4\ cm)^{2}=4\cdot25\ cm^{2}-11,56\ cm^{2}=\boxed{88,44\ cm^{2}}[/tex]
[tex]b) \ P=\boxed{b\cdot(8-a)}\\\\dla \ a=0,5\ dm=5\ cm\ i \ b=3,4\ cm:\\\\P=3,4\ cm\cdot(8\ cm-5\ cm)=3,4\ cm\cdot3\ cm=\boxed{10,2\ cm^{2}}[/tex]
