P= 2•l+2•L
Sp= 456:2
Sp=258
Sp=l+L
258=l+l+28
2•l=258-28
2•l=200
l=200:2
l=100
L=100+28
L=128
Sp= semiperimedtru adica lungime plus latimea.
L-l=28 =>L=l+28
P dreptunghi=2xL+2xl
P=2x(l+28)+2xl=2l+56+2l=4l+56=456=>4l=456-56=400=>l=100=>L=100+28=128