Answer:
∠4 = a + b
Step-by-step explanation:
Given ∠2 = a and ∠3 = b
The sum of the 3 angles in a triangle = 180°
Subtract the sum of the 2 given angles from 180 for ∠1
∠1 = 180 - (a + b) = 180 - a - b
Now
∠1 and ∠4 form a straight angle and are supplementary, hence
∠4 = 180 - (180 - a - b) = 180 - 180 + a + b = a + b
