1.3x+13=31
3x=31-13
3x=18
x=18:3
x=6
2.[tex] \frac{l}{L} = \frac{4}{5} [/tex]
[tex] \frac{l}{20}= \frac{4}{5} [/tex]
[tex]l=4*4=16cm[/tex]
[tex]P=(l+L)*2=(16+20)*2=36*2=72cm[/tex]
3.[tex]13 ^{2} =5 ^{2} +12[/tex]
[tex]169=125+44[/tex]
[tex]169=169=\ \textgreater \ tringhiul ABC este dreptunghic[/tex]
4.[tex]A_{ABCD} = \frac{AC*BD}{2} = \frac{14*20}{2} =140[/tex]
