In figure 9.39, AB ∥ DE. Find ∠ACD.
Question:
In figure 9.39, AB ∥ DE. Find ∠ACD.

Solution:
Since AB ∥ DE
∴ ∠ABC = ∠CDE = 40° [Alternate angles]
∴ ∠ACB = 180° − ∠ABC − ∠BAC
=180° − 40° − 30°
= 110°
∴ ∠ACD = 180° − 110° [Linear pair]
= 70°