If the angle of vertex of an isosceles triangle is 100∘, then the measure of a base angle equals .
A
40∘
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B
80∘
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C
20∘
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Solution
The correct option is A40∘ Given that ∠A=100∘ Since △ABC is isosceles, we have ∠ABC=∠ACB=x(say) Now, ∠x+∠x+100∘=180∘(Using angle sum property) ⟹2x+100∘=180∘ ⟹2x=80∘⟹x=40∘