Răspuns:
BE _l_ CD ( E apartine CD) ; AF_l_ CD
BEC = dreptunghic; <) C =60 grade => <)CBE =30 grade
CE=DF = (CD-AB) : 2
CE =( 20-8) : 2 =6
CE =BC/2 (teorema <) de 30 grade)
6=BC/2
BC =6*2 =12 cm ; BC=AD ( trapez isoscel)
Pabcd =8+12+20+12 =52 cm
Explicație pas cu pas: