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Mathematics

Solve the following equation for x and give your answer correct to two decimal places :

x2 - 5x - 10 = 0

Quadratic Equations

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Answer

Comparing x2 - 5x - 10 = 0 with ax2 + bx + c = 0 we get,

a = 1, b = -5 and c = -10.

We know that,

x = b±b24ac2a\dfrac{-b \pm \sqrt{b^2 - 4ac}}{2a}

Substituting values of a, b and c in above equation we get,

x=(5)±(5)24.(1).(10)2(1)=5±25+402=5±652=5±8.062=5+8.062 and 58.062=13.062 and 3.062=6.53 and 1.53\Rightarrow x = \dfrac{-(-5) \pm \sqrt{(-5)^2 - 4.(1).(-10)}}{2(1)} \\[1em] = \dfrac{5 \pm \sqrt{25 + 40}}{2} \\[1em] = \dfrac{5 \pm \sqrt{65}}{2} \\[1em] = \dfrac{5 \pm 8.06}{2} \\[1em] = \dfrac{5 + 8.06}{2} \text{ and } \dfrac{5 - 8.06}{2} \\[1em] = \dfrac{13.06}{2} \text{ and } \dfrac{-3.06}{2} \\[1em] = 6.53 \text{ and } -1.53

Hence, x = 6.53 and -1.53

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