Question 14

If in an isosceles triangle, each of the base angle is $40^{\circ}$ , then the triangle is

a) Right angled triangle
b) Acute angled triangle
c) Obtuse-angled triangle
d) Isosceles right-angled triangle

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Solution

As we know, the sum of the interior angles of a triangle is $180^{\circ}$

In $Δ A B C$ ,
$∠ A + ∠ B + ∠ C = 180^{\circ}$ [angle sum property of a triangle]
$\Rightarrow ∠ A + 40^{\circ} + 40^{\circ} = 180^{\circ} \Rightarrow ∠ A = 180^{\circ} - 80^{\circ}$
$\Rightarrow ∠ A = 100^{\circ}$ [obtuse angle]
Therefore, it is an obtuse angled triangle, since it has one angle which is greater than $90^{\circ}$

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Question 14 If in an isosceles triangle, each of the base angle is 40∘, then the triangle is a) Right angled triangle b) Acute angled triangle c) Obtuse-angled triangle d) Isosceles right-angled triangle

Question 14

If in an isosceles triangle, each of the base angle is $40^{\circ}$ , then the triangle is

a) Right angled triangle
b) Acute angled triangle
c) Obtuse-angled triangle
d) Isosceles right-angled triangle