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Triangles — MATHS STD 9 — Question

Rajasthan BoardEnglish MediumSTD 9MATHSTriangles1 Mark
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Answer

  1. 110º
    Solution:

    If $\text{AE}\parallel\text{DC}$ and AC is transversal,
    then $\angle\text{FAC}=70^\circ$ (opposite angles)
    Also $\angle\text{FAC}-=\angle\text{ACB}=70^\circ$ (Alternate angles)
    Since $\text{AB}=\text{AC},\triangle\text{ABC}$ is isosceles.
    So $\angle\text{ABC}=\angle\text{ACB}$
    $\Rightarrow\angle\text{ABC}=70^\circ$
    Now $\angle\text{ABD}=180^\circ-\angle\text{ABC}=180^\circ-70^\circ=100^\circ$
    Hence, correct option is (b).

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