JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Solution of quadratic equations and Nature of roots

  • question_answer
    If \[a>0,b>0,c>0\] then both the roots of the equation \[a{{x}^{2}}+bx+c=0\]

    A) Are real and negative

    B) Have negative real parts

    C) Are rational numbers

    D) None of these

    Correct Answer: B

    Solution :

    The roots of the equations are given by \[x=\frac{-b\pm \sqrt{{{b}^{2}}-4ac}}{2a}\] (i)   Let \[{{b}^{2}}-4ac>0,b>0\]       Now if \[a>0,c>0,{{b}^{2}}-4ac<{{b}^{2}}\]        Þ the roots are negative. (ii)  Let \[{{b}^{2}}-4ac<0,\] then the roots are given by       \[x=\frac{-b\pm i\sqrt{(4ac-{{b}^{2}})}}{2a},\,\,\,\,\,\,(i=\sqrt{-1})\]      Which are imaginary and have negative real part\[(\because \,\,b>0)\]     \ In each case, the roots have negative real part.


You need to login to perform this action.
You will be redirected in 3 sec spinner