Question

if m∠acb = 180°, and m∠acd = 120° then m∠dcb = ?°

Explanation:

Step1: Identify angle - relationship

$\angle ACB=\angle ACD+\angle DCB$

Step2: Solve for $\angle DCB$

$\angle DCB=\angle ACB - \angle ACD$
Substitute $\angle ACB = 180^{\circ}$ and $\angle ACD=120^{\circ}$ into the formula: $\angle DCB=180^{\circ}- 120^{\circ}=60^{\circ}$

Answer:

$60$