Answer:
m ∠ 1 = 140°
Step-by-step explanation:
In ∆ABC
m ∠B = 180° - 60° = 120°
Being a linear pair, in which the sum of pairs of angles in a straight line are supplementary.
As, we know that
Exterior angle of a triangle is equal to the sum of two opposite remote angle.
m ∠ 1 = m ∠B + m ∠A
Substitute the value:
m ∠ 1 = 120° + 20°
m ∠ 1 = 140°
Therefore, the value of m ∠ 1 is 140°
