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Question
In a ΔABC, if AB = AC and ∠B = 70°, find ∠A.
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Solution
Consider , ΔABC we have `∠B=70^@` and AB =AC
Since, AB A C ABC is an isosceles triangle
⇒ ∠B=∠C [Angles opposite to equal sides are equal]
⇒`∠B = ∠C = 70^@`
And also,
Sum of angles in a triangle `180^@`
⇒ `∠A+∠B+∠C=180^@`
⇒`∠A+70^@+70^@=180^@`
⇒`∠A+140^@=180^@`
⇒`∠A=180^@-140^@⇒∠A=40^@`
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