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Show that the angles of an equilateral triangle are 60° each.

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Define the same as each of the other two angles in the equilateral triangle.
NCERT Books for Session 2022-2023 are based on CBSE Board.
Important Triangles Solutions for class 9th Exercise 7.2, Question no: 8.

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1 Answer

  1. In ΔABC,
    AB = AC [∵ Given]
    ∠C = ∠B …(1) [∵ Angles opposite to equal sides are equal]
    Similarly,
    In ΔABC,
    AB = BC [∵ Given]
    ∠C = ∠A …(2) [∵ Angles opposite to equal sides are equal]
    From the equation (1) and (2), we have

    ∠A = ∠B = ∠C …(3)
    In ΔABC,
    ∠A + ∠B + C = 180°
    ⇒ ∠A +∠A+ ∠A= 180° [∵ From the equation (3)]
    ⇒ 3∠A = 180°
    ⇒ ∠A = (180°/3) = 60°
    Hence, ∠A = ∠B = ∠C = 60°.

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