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What are the roots of the equation x^2-9x-10?(a) 9, 1(b) -9, -1(c) -10, 1(d) 10, -1This question was addressed to me in an interview for job.The above asked question is from Solution of Quadratic Equation by Squaring Method topic in chapter Quadratic Equation of Mathematics – Class 10

Answer»

The correct choice is (d) 10, -1

The best EXPLANATION: x^2-9X-10=0

Shifting -10 to RHS

x^2-9x=10

Adding \(\frac {b^2}{4}\) on both SIDES, where b=-9

x^2 – 9x + \(\frac {-9^2}{4} = \frac {-9^2}{4}\) + 10

x^2 – 9x + \(\frac {81}{4} = \frac {81}{4}\) + 10

x^2 – 9x + \(\frac {81}{4} = \frac {121}{4}\)

\((x-\frac {9}{2})\)^2=\((\frac {11}{2})\)^2

x – \(\frac {9}{2}\) = ± \(\frac {11}{2}\)

x = \(\frac {11}{2}+\frac {9}{2}=\frac {20}{2}\) = 10 and x = \(\frac {-11}{2} + \frac {9}{2} = \frac {-2}{2}\) = -1

The roots of the equation are 10 and -1.


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