9th Class Mathematics Quadrilaterals Question Bank Quadrilateral

  • question_answer
    The sides BA and DC of quadrilateral ABCD are produced as shown la figure. Them which of the following statements is correct?

    A)  \[2{{x}^{{}^\circ }}+{{y}^{{}^\circ }}={{a}^{{}^\circ }}+{{b}^{{}^\circ }}\]            

    B)  \[{{x}^{{}^\circ }}+\frac{1}{2}{{y}^{{}^\circ }}=\frac{{{a}^{{}^\circ }}+{{b}^{{}^\circ }}}{2}\]

    C)  \[{{x}^{{}^\circ }}+{{y}^{{}^\circ }}={{a}^{{}^\circ }}+{{b}^{{}^\circ }}\] 

    D)  \[{{x}^{{}^\circ }}+{{a}^{{}^\circ }}={{y}^{{}^\circ }}+{{b}^{{}^\circ }}\]

    Correct Answer: C

    Solution :

    (c):   As \[{{a}^{{}^\circ }}+{{b}^{{}^\circ }}={{180}^{{}^\circ }}\] \[\Rightarrow \]\[\angle A={{180}^{{}^\circ }}-b\] Also, \[\angle C+{{a}^{{}^\circ }}={{180}^{{}^\circ }}\](linear pair) \[\Rightarrow \]\[\angle C={{180}^{{}^\circ }}-{{a}^{{}^\circ }}\] But \[\angle A+\angle B+\angle C+\angle D~={{360}^{{}^\circ }}\] \[\Rightarrow \]\[\left( {{180}^{{}^\circ }}-{{b}^{{}^\circ }} \right)+x+\left( {{180}^{{}^\circ }}-{{a}^{{}^\circ }} \right)+{{y}^{{}^\circ }}={{360}^{{}^\circ }}\] \[\Rightarrow \]\[{{x}^{{}^\circ }}+{{y}^{{}^\circ }}={{a}^{{}^\circ }}+{{b}^{{}^\circ }}\]                


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