Question

if m∠acd = 100°, then m∠ecb = ?°.

Explanation:

Step1: Identify intersecting lines

Two lines intersect at C, forming vertical angles.

Step2: Recognize vertical angles

∠ACD and ∠ECB are vertical angles (opposite at intersection).

Step3: Apply vertical angle theorem

Vertical angles are equal, so m∠ECB = m∠ACD.

Step4: Substitute given value

m∠ACD = 100°, thus m∠ECB = 100°.

Answer:

100