perim bazei=12⇒l=perim:3=4
si latura bazei/2=4/2=2
aria unei fete laterale= latura bazei * apotema/2
20=4*apotema/2=2*apoteama⇒apotema=10
muchia laterala = (Pitagora )=
√(apotema ²+ (latbazei/2)²)=√(10²+2²)=√104=2√26
3 muchii lateral=3*2√26=6√26
suma muchiilor=12+3√26