8th Class Mathematics Understanding Quadrilaterals Question Bank Understanding Quadrilaterals

  • question_answer
    ABCD is a parallelogram. Find the angles x, y and z in the given figure,

    A)  \[40{}^\circ ,\text{ }50{}^\circ ,\text{ }60{}^\circ \]

    B)  \[60{}^\circ ,\text{ }60{}^\circ ,\text{ }60{}^\circ \]

    C)  \[50{}^\circ ,\text{ }50{}^\circ ,\text{ }60{}^\circ \]

    D)  \[60{}^\circ ,\text{ }70{}^\circ ,\text{ }70{}^\circ \]

    Correct Answer: C

    Solution :

    Since, ABCD is a parallelogram \[\therefore \angle ADC=\angle ABC\Rightarrow x=z~~~~~~...(i)\] Now in right triangle EBC, we have \[\angle \text{BEC+}\angle \text{EBC+}\angle \text{ECB=180 }\!\!{}^\circ\!\!\text{ }\] \[\Rightarrow 90{}^\circ +x+40{}^\circ =180{}^\circ \] \[\Rightarrow x=180{}^\circ -130{}^\circ =50{}^\circ \] From (i), \[x\text{ }=\text{ }z\text{ }=\text{ }50{}^\circ \] Now, in\[\Delta FCD\], we have \[\angle CFD+\angle FDC+\angle FCD=180{}^\circ \]                         [Angle sum property] \[\Rightarrow 90{}^\circ +50{}^\circ +\angle FCD=180{}^\circ \] \[\Rightarrow 140{}^\circ +\angle FCD=180{}^\circ \] \[\Rightarrow \angle FCD=180{}^\circ -140{}^\circ =40{}^\circ \] Also, in parallelogram ABCD, we have \[\angle ADC+\angle DCB=180{}^\circ \] \[\Rightarrow 50{}^\circ +(\angle FCD+y+40{}^\circ )=180{}^\circ \] \[\Rightarrow 50{}^\circ +40{}^\circ +y+40{}^\circ =180{}^\circ \] \[\Rightarrow y=180{}^\circ -130{}^\circ \Rightarrow y=50{}^\circ \] \[\therefore x=y=z=50{}^\circ \]


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