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Mathematics

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

4x2 - 5x - 3 = 0

Quadratic Equations

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Answer

Comparing 4x2 - 5x - 3 = 0 with ax2 + bx + c = 0 we get,

a = 4, b = -5 and c = -3.

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.(4).(3)2(4)=5±25+488=5±738=5±8.548=5+8.548 and 58.548=13.548 and 3.548=1.69 and 0.44\Rightarrow x = \dfrac{-(-5) \pm \sqrt{(-5)^2 - 4.(4).(-3)}}{2(4)} \\[1em] = \dfrac{5 \pm \sqrt{25 + 48}}{8} \\[1em] = \dfrac{5 \pm \sqrt{73}}{8} \\[1em] = \dfrac{5 \pm 8.54}{8} \\[1em] = \dfrac{5 + 8.54}{8} \text{ and } \dfrac{5 - 8.54}{8} \\[1em] = \dfrac{13.54}{8} \text{ and } \dfrac{-3.54}{8} \\[1em] = 1.69 \text{ and } -0.44

Hence, x = 1.69 and -0.44

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