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Triangles — MATHS STD 9 — Question

Rajasthan BoardEnglish MediumSTD 9MATHSTriangles1 Mark
Question
It is given that $\triangle\text{ABC} ≅\triangle\text{FDE}$ and AB = 5cm, $\angle\text{B} = 40^\circ$ and $\angle\text{A} = 80^\circ$ Then which of the following is true?
✓

Answer

  1. $\text{DF} = 5\text{cm}, \ \angle\text{E} = 60^\circ$
    Solution:
    Given that: In $\triangle\text{ABC}, \ \text{AB} = 5\text{cm},\ \angle\text{B} = 40^\circ$ and $\angle\text{A} = 80^\circ$
    Using angles sum property of triangle, we have
    $\angle\text{A} + \angle\text{B} + \angle\text{C} = 180^\circ$
    $⇒ 80^\circ + 40^\circ + \angle\text{C} = 180^\circ$
    $⇒ 120^\circ + \angle\text{C} = 180^\circ$ [$\therefore\ \angle\text{B} = 40^\circ$ and $\angle\text{A} = 80^\circ$]
    $⇒ \angle\text{C} = 180^\circ – 120^\circ$
    $⇒ \angle\text{C} = 60^\circ$
    It is given that $\triangle\text{ABC} ≅\triangle\text{FDE},$ so we have
    AB = FD, BC = DE and $\text{AC}=\text{FE}\ \&\ \angle\text{A} = \angle\text{F}, \ \angle\text{B} = \angle\text{D}$ and $\angle\text{C} =
    \angle\text{E}$
    ⇒ AB = FD = 5cm and $\angle\text{C} = \angle\text{E} = 60^\circ$

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