MCQ
Mark $(\checkmark)$ against the correct answer.In $\triangle\text{ABC}$ if $\angle\text{A}=65^\circ$ and $\angle\text{C}=85^\circ$ then $\angle\text{B}={}?$
- A$25^\circ$
- ✓$30^\circ$
- C$35^\circ$
- D$40^\circ$
✓
Answer
Correct option: B.
$30^\circ$
In $\triangle\text{ABC}$
$\angle\text{A}=65^\circ,\angle\text{C}=85^\circ$
But $\angle\text{A}+\angle\text{B}+\angle\text{C}=180^\circ$ (Angles of a triangle)
$\Rightarrow65^\circ+\angle\text{B}+85^\circ=180^\circ$
$\Rightarrow150^\circ+\angle\text{B}=180^\circ$
$\Rightarrow\angle\text{B}=180^\circ-150^\circ=30^\circ$
$\angle\text{A}=65^\circ,\angle\text{C}=85^\circ$
But $\angle\text{A}+\angle\text{B}+\angle\text{C}=180^\circ$ (Angles of a triangle)
$\Rightarrow65^\circ+\angle\text{B}+85^\circ=180^\circ$
$\Rightarrow150^\circ+\angle\text{B}=180^\circ$
$\Rightarrow\angle\text{B}=180^\circ-150^\circ=30^\circ$
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