\(S_{SFTE}=1260\left(dm^2\right)\)
=>\(FX\cdot SE=1260\)
=>\(35\cdot SE=1260\)
=>SE=1260/35=36(dm)
\(FY=\dfrac{4}{5}\cdot FX=\dfrac{4}{5}\cdot35=28\left(dm\right)\)
\(S_{SFTE}=FY\cdot ET\)
=>\(28\cdot ET=1260\)
=>ET=1260/28=45(dm)
Chu vi hình bình hành SFTE là:
2(ET+SE)=2(45+36)=2*81=162(dm)