Salut,
Fie paralelogramul ABCD;
m(<B)=m(<D)=135°
m(<A)=m(<C)=(360°-(135°*2))/2=(360°-270°)/2=90°/2=45°;
A=AD*BK;BK-inaltimea paralelogramului;
40=10*BK
BK=40/10
BK=4(cm);
sin45°⇒BK=√2/2*AB⇒AB=BK*√2;
AB=4√2(cm);
P=2AB+2AD;
P=2*4√2+2*10=(8√2+20)cm;
Raspuns:P=(8√2+20)cm.
Bafta!