duc BNperpendicular pe DA; N apartine DA
ΔBNA: ∡A=45
∡N=90 din ambele => ∡NBA=45=> ΔBNA isoscel=> BN=NA
BN²+NA²=BA²
2BN²=(4√2)²
2BN²=√32²
2BN²=32=>BN²=32:2=> BN²16=>BN=√16=> BN=4
daca BN=4> NA=4
DN+NA=DA
DN+4=8
DN=8-4
DN=4
CDNB este patrat=> cd=cb=4
petrimetrul trapezului=CD+DA+AB+CB=4+8+4√2+4=16+4√2=2(4+√2)
