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Question
If in an isosceles triangle, each of the base angles is 40°, then the triangle is ______.
Options
Right-angled triangle
Acute angled triangle
Obtuse angled triangle
Isosceles right-angled triangle
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Solution
If in an isosceles triangle, each of the base angles is 40°, then the triangle is obtuse angled triangle.
Explanation:
As we know, the sum of the interior angles of a triangle is 180°.
In ΔABC,
∠A + ∠B + ∠C = 180° ...[Angle sum property of a triangle]
⇒ ∠A + 40° + 40° = 180°
⇒ ∠A = 180° – 80°
⇒ ∠A = 100° ...[Obtuse angle]
Therefore, it is an obtuse-angled triangle. Since, it has one angle which is greater than 90°.
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