Question
In $\triangle\text{ABC, AB = AC}$ and $\angle\text{B}=50^{\circ}.$ Then, $\angle\text{A = } ?$
- 40°
- 50°
- 80°
- 130°
✓
Answer
- 80°
In $\triangle\text{ABC,}$
$\text{AB = AC}$
$\Rightarrow\angle\text{C}=\angle\text{B}$ (angles opposite to equal sides are equal)
$\Rightarrow\angle\text{C}=50^{\circ}$
Now, $\angle\text{A}+\angle\text{B}+\angle\text{C}=180^{\circ}$
$\Rightarrow\angle\text{A}+50^{\circ}+50^{\circ}=180^{\circ}$
$\Rightarrow\angle\text{A}=80^{\circ}$
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