求角B的度数---**Question Stem:** 在△ABC中，点D在BC上，AC+CD=AB，∠ADC=70°，∠ACB=80°，求∠B的度数 **Mathematical Formulas/Equations from Stem:** * `AC + CD = AB` * `∠ADC = 70°` * `∠ACB = 80°` * `求∠B的度数` (Find the measure of angle B) **Chart/Diagram Description:** * **Type:** Geometric figure (triangle). * **Main Elements:** * **Points:** There are four labeled points: A, B, C, and D. * **Lines:** * Three main segments form triangle ABC: AB, BC, CA. * An additional segment AD connects vertex A to point D on BC. * **Shapes:** The diagram shows a large triangle ABC, which is divided into two smaller triangles, ABD and ADC, by the segment AD. * **Relative Position:** Point D is located on the line segment BC, between points B and C. Point A is above the line segment BC. * **Angles and Labels:** * The angle at vertex B (∠ABC or simply ∠B) is marked with a question mark (?). * The angle ∠ADC (at point D, within triangle ADC) is labeled as 70°. * The angle ∠ACB (at vertex C, within triangle ABC) is labeled as 80°.