Answer:
x = 20
Step-by-step explanation:
The sum of the 3 angles in a triangle = 180°
Using ΔAHC , then
∠ACH = 180 - (2x + 100) = 180 - 2x - 100 = 80 - 2x
∠ECD = ∠ACB ( vertical angles are congruent ), thus
∠ECD = ∠ACH + ∠HCB, that is
3x = 80 - 2x + x
3x = 80 - x ( add x to both sides )
4x = 80 ( divide both sides by 4 )
x = 20
