Answer

  1. x + y - 180
    Solution:
    In the given figure, $\angle\text{ABF}+\angle\text{ABC}=180^\circ$ (Linear pair of angles)
    $∴\text{x}^\circ+\angle\text{ABC}=180^\circ$
    $⇒\angle\text{ABC}=180^\circ−\text{x}°...\ (\text{i})$
    Also, $\angle\text{ACG}+\angle\text{ACB}=180^\circ$ (Linear pair of angles)
    $∴\text{y}′+\angle\text{ACB}=180^\circ$
    $⇒\angle\text{ACB}=180^\circ−\text{y}′\ ...\ \text{(ii)}$
    Also, $\angle\text{BAC}=\angle\text{DAE}=\text{z}° \ ....\ \text{(iii)}$ (Vertically opposite angles)
    In $\triangle\text{ABC}$
    $\angle\text{BAC}+\angle\text{ABC}+\angle\text{ACB}=180^\circ$ (Angle sum property)
    $∴\text{z}^\circ+180−\text{x}^\circ+180^\circ−\text{y}^\circ=180^\circ$ [Using (1), (2) and (3)]
    $⇒ \text{z} = \text{x} + \text{y} – 180$

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