In the figure, AC = DE = 7 cm. If BD = 4 cm, then CF equals
4 cm
Construction: Extend ED to G, where it cuts AB. Similarly, extend AC to cut EF at H.
∠EDF=∠BCA [Given]
Given, AB∥EF.
∠DEF=∠DGB ⋯ (1)
(Alternate interior angles)
Since AC∥DE, we must have
∠DGB=∠BAC⋯ (2) (Corresponding angles)
From (1) and (2),
∠DEF=∠BAC
In ΔABC and ΔEFD,
∠ACB=∠EDF [Given]
∠BAC=∠DEF [Proven]
AC = DE [Given]
⟹ΔABC≅ΔEFD (AAS congruency criteria)
So, BC = DF [CPCT]
⟹ BC - DC = DF - DC
⟹ BD = CF
⟹ CF = 4 cm [∵ BD = 4 cm (given)]