Question

4 The vertical angle of an isosceles triangle is 100". Find Its base angles


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Answer 1

Isosceles triangles have 2 angles equal
Therefore by angle sum property of triangle:
100+2x=180
2x=80
x=40

Answer 2

Consider an isosceles ΔABC such that AB=AC Given that vertical angle A is 100°. Given to find the base angles Since ΔABC is isosceles ∠B=∠C [Angles opposite to equal angles are equal] And also, Sum of the interior angles of a triangle = 180°

<A+<B+<C=180°

100°+<B+<B=180°

2<B=180°-100°

2<B=80°

<B=80°÷2=40°

<B=<C=40°

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