MCQ
In the following, write the correct answer. In $\triangle\text{ABC}$ if $BC = AB$ and $\angle\text{B}=80^{\circ}$ then is equal to:
- A$80^\circ$
- B$40^\circ$
- ✓$50^\circ$
- D$100^\circ$
✓
Answer
Correct option: C.
$50^\circ$
In $\triangle\text{ABC}$ we have
$BC = AB$ But $\angle\text{B}=80^{\circ}$
$\angle\text{A}+\angle\text{B}+\angle\text{C}=180^{\circ}$
$=\angle\text{A}+80^{\circ}\angle\text{A}=180^{\circ}$
$=2\angle\text{A}=100^{\circ}$
$=\angle\text{A}=100^{\circ}\div2=50^{\circ}$
$BC = AB$ But $\angle\text{B}=80^{\circ}$
$\angle\text{A}+\angle\text{B}+\angle\text{C}=180^{\circ}$
$=\angle\text{A}+80^{\circ}\angle\text{A}=180^{\circ}$
$=2\angle\text{A}=100^{\circ}$
$=\angle\text{A}=100^{\circ}\div2=50^{\circ}$
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