9th Class Mathematics Triangles Question Bank Triangle

  • question_answer
    The lengths of the sides of a triangle is x, y mid z respectively. If \[{{\mathbf{x}}^{\mathbf{2}}}\mathbf{+}{{\mathbf{y}}^{\mathbf{2}}}\mathbf{+}{{\mathbf{z}}^{\mathbf{2}}}\mathbf{=xy+yz+xz,}\] then the triangle is:

    A)  Isosceles                      

    B)  Equilateral

    C)  Scalene                       

    D)  Right - angled

    Correct Answer: B

    Solution :

    (b): \[{{x}^{2}}+{{y}^{2}}+{{z}^{2}}=xy+yz+zx,\] \[\Rightarrow \] \[2{{x}^{2}}+2{{y}^{2}}+2{{z}^{2}}=2xy+2yz+2zx\] \[\Rightarrow \]\[{{x}^{2}}+{{y}^{2}}-2xy+{{y}^{2}}+{{z}^{2}}-2yz+{{z}^{2}}+{{x}^{2}}-2zx=0\] \[\Rightarrow \]\[{{(x-y)}^{2}}+{{(y-z)}^{2}}+{{(z-x)}^{2}}=0\] \[\therefore \] \[x-y=0\Rightarrow x=y\] \[y-z=0\Rightarrow y=z\] \[z~-x=0\Rightarrow z=x\] \[\therefore \]\[x=y=z\] \[\therefore \] It is an equilateral triangle.


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