ΔABC ∼ ΔEDF Area ABC : Area DEF = 49 : 4. If AB, AC, BC are, respectively, 10 cm, 14 cm, 21 cm, then what is the length (in cm) of EF?

4.5 6 3.5 4

4

We know that, ΔABC ~ ΔEDF, We have, Area ABC ∶ Area DEF = 49 ∶ 4 AB = 10 cm AC = 14 cm BC = 21 cm  Area ABC/Area DEF = (AC/EF)2 = 49/4 = (AC/EF)2 = 7/2 = 14/EF  = 1/2 = 2/EF  EF = 4 cm