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a. P=28=2L+2l
L=2.5l inlocuim
28=2*2.5l+2l=7l =>l=4dm si L=4*2.5=10dm
A=4*10=40dm²
b. fie BE ⊥ CD , EC=10-7=3cm, cum ∡C=45°⇒ΔBCE=dreptunghic isoscel si BE=3cm deci At=3*3/2=4.5cm²
Ad=7*3=21cm²
At=21+4.5=25.5cm²