m∠8 = 78°
Solution:
Given Line a is parallel to line b.
Measure of ∠2 = 78°
Let us first find the measure of ∠4.
Vertically opposite angles are equal.
⇒ m∠2 = m∠4
∴ m∠4 = 78°
We know that if a and b are parallel line cut by a transversal, then the corresponding angles on the same side of the transversal are equal.
Here, ∠4 is the corresponding angle of ∠8.
⇒ m∠4 = m∠8
∴ m∠8 = 78°
Hence, the measure of ∠8 is 78°.