Question

In $△ABC$, $AB=AC$ and $\angle B={40}^{\circ }$. What type of triangle is this ?

• A. 6m, equilateral triangle
• B. 4 m, Isosceles triangle
• C. 6 m, Isosceles triangle
• D. 4 m, equilateral triangle

Answer 1

Answer: (A), (B)

The correct options are
A

6m, equilateral triangle

B

4 m, Isosceles triangle

Since AB = AC, the angles opposite these sides will also be equal.
As AB = AC it is an isosceles triangle.

Hence, $\angle B=\angle C$

$\Rightarrow \angle C={40}^{\circ }$

$\angle A={180}^{\circ }-(\angle B+\angle C)$

$\angle A={180}^{\circ }-{80}^{\circ }$

$\angle A={100}^{\circ }$

Therefore, this is an obtuse angled triangle.