Question

In $∆$ABC, seg AB $\cong$ seg AC and $\angle$A = 80$°$ then find $\angle$B and $\angle$C

Answer 1

$$\begin{gathered} \mathrm{Given}:\mathrm{In}△\mathrm{ABC}, \\ \mathrm{seg}\mathrm{AB}\cong \mathrm{seg}\hspace{0.17em}\mathrm{AC}\Rightarrow \angle \mathrm{B}=\angle \mathrm{C}...\left(\mathrm{i}\right) \\ \angle \mathrm{A}=80°.....\left(\mathrm{ii}\right) \\ \mathrm{We}\mathrm{know}\mathrm{that} \\ \angle \mathrm{A}+\angle \mathrm{B}+\angle \mathrm{C}=180°(\text{a}\mathrm{ngle}\mathrm{sum}\mathrm{property}) \\ \Rightarrow 80°+2\angle \mathrm{B}=180°(\mathrm{from}(\mathrm{i})\mathrm{and}(\mathrm{ii}\left)\right) \\ \Rightarrow 2\angle \mathrm{B}=100° \\ \Rightarrow \angle \mathrm{B}=50°=\angle \mathrm{C} \end{gathered}$$