10th Class Mathematics Quadratic Equations Question Bank Quadratic Equations

  • question_answer
    If the roots of the equation \[(a-b){{x}^{2}}+(b-c)x+(c-a)=0\] are equal. Then _______.

    A)  \[2b=a+c\]               

    B)  \[2a=b+c\] 

    C)         \[2c=a+b\]     

    D)         \[\frac{1}{b}=\frac{1}{a}+\frac{1}{c}\]  

    Correct Answer: B

    Solution :

    Since the given equation has equal roots, \[\therefore \]  \[D=0\] \[\Rightarrow \]   \[{{(b-c)}^{2}}-4(c-a)\,(a-b)=0\] \[\Rightarrow \] \[4{{a}^{2}}+{{b}^{2}}+{{c}^{2}}-4ab+2bc-4ac=0\] \[\Rightarrow \] \[{{(-2a)}^{2}}+({{b}^{2}})+{{(c)}^{2}}+2(-2a)(b)+2bc\]                                     \[+2(-2a)\,(c)=0\] \[\Rightarrow \]   \[{{(-2a+b+c)}^{2}}=0\] \[\Rightarrow \] \[-2a+b+c=0\]  \[\Rightarrow \]\[2a=b+c\]


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