9th Class Mathematics Areas of Parallelograms and Triangles Question Bank Areas of Parallelograms and Triangles

  • question_answer
    In the given figure, ABCD is a parallelogram and P is mid-point of AB. If \[(APCD)=36\,c{{m}^{2}},\]then \[ar\,(\Delta ABC)=\]

    A) \[36\text{ }c{{m}^{2}}\]               

    B)        \[~48\,c{{m}^{2}}\]               

    C)                    \[24\text{ }c{{m}^{2}}\]                     

    D)         None of these        

    Correct Answer: C

    Solution :

    Since, diagonals of a parallelogram divides it into two triangles of equal areas. \[\therefore \]\[ar(\Delta \Alpha BC)=\frac{1}{2}ar(ABCD)\] \[\Rightarrow \]\[2ar(\Delta \Alpha \Beta C)=ar(ABCD)\] \[\Rightarrow \]\[2ar(\Delta \Alpha \Beta C)=ar(APCD)+ar(\Delta PBC)\] \[\Rightarrow \]\[2ar(\Delta \Alpha \Beta C)=36+ar(\Delta PBC)\]     ?(i) CP is the median of \[\Delta \Alpha CB,\]and median divides a triangle into two triangles of equal area. \[\therefore \]\[ar(\Delta PBC)=\frac{1}{2}ar(\Delta \Alpha \Beta C)\]                       ?(ii) Now, from (i) and (ii), we get \[2ar(\Delta \Alpha \Beta C)=36+\frac{1}{2}ar(\Delta \Alpha \Beta C)\] \[\Rightarrow \]\[2\,ar\,(\Delta \Alpha \Beta C)-\frac{1}{2}ar(\Delta \Alpha \Beta C)=36\] \[\Rightarrow \]\[\frac{3}{2}ar(\Delta \Alpha \Beta C)=36\] \[\Rightarrow \]\[ar(\Delta \Alpha \Beta C)=\frac{36\times 2}{3}=24\,c{{m}^{2}}\]


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