Ipoteza:
ABCD trapez dreptunghic
AB||CD
AB<CD
m(<ABC)=120
AB=4cm
BC=8cm(4)
Concluzie:
CD=?
BD=?
a)Construim inaltimea [BS].
m(<ABS)=90;m(<ABC)=120=>m(<SBC)=120-90=30(1) ; m(<C)=90-30=60(5)
ΔSBC dreptunghic in S.(2)
Din(1),(2)=>SC=BC/2=4cm.
DS=AB=4cm
CD=DS+SC=8cm(3)
b)Din (3),(4)=>ΔBDC isoscel(6)
Din (5),(6)=>ΔBDC echilateral =>BD=8cm
