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4-2.Quadratic Equations and Inequations
medium
The product of all real roots of the equation ${x^2} - |x| - \,6 = 0$ is
A$-9$
B$6$
C$9$
D$36$
Solution
(a) Given equation ${x^2} – |x| – 6 = 0$
If $x > 0$, equation is ${x^2} – x – 6 = 0$
==> $(x – 3)(x + 2) = 0$
==> $x = 3,\,x = – 2$
==> $x = 3$
If $x < 0$, equation is ${x^2} + x – 6 = 0$
==> $(x + 3)(x – 2) = 0$
==> $x = – 3,\,x = 2$
==> $x = – 3$
Hence product of all possible real roots $= -9.$
If $x > 0$, equation is ${x^2} – x – 6 = 0$
==> $(x – 3)(x + 2) = 0$
==> $x = 3,\,x = – 2$
==> $x = 3$
If $x < 0$, equation is ${x^2} + x – 6 = 0$
==> $(x + 3)(x – 2) = 0$
==> $x = – 3,\,x = 2$
==> $x = – 3$
Hence product of all possible real roots $= -9.$
Standard 11
Mathematics