Without using a calculator, find the values of aa and bb for which the solution of the equation x24=x3+6x\sqrt{24} = x\sqrt{3} + \sqrt{6} is a+b7\frac{a + \sqrt{b}}{7}.

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Worked solution

2

1. Rearrange the equation to make $x$ the subject.

x24−x3=6x\sqrt{24} - x\sqrt{3} = \sqrt{6}
x(24−3)=6x(\sqrt{24} - \sqrt{3}) = \sqrt{6}
x=624−3x = \frac{\sqrt{6}}{\sqrt{24} - \sqrt{3}}

2. Rationalise the denominator by multiplying the numerator and denominator by the conjugate.

x=6(24+3)(24−3)(24+3)x = \frac{\sqrt{6}(\sqrt{24} + \sqrt{3})}{(\sqrt{24} - \sqrt{3})(\sqrt{24} + \sqrt{3})}

3. Expand and simplify the numerator and denominator.

x=144+1824−3x = \frac{\sqrt{144} + \sqrt{18}}{24 - 3}
x=12+9×221x = \frac{12 + \sqrt{9 \times 2}}{21}
x=12+3221x = \frac{12 + 3\sqrt{2}}{21}

4. Simplify the fraction and compare with the given form to find $a$ and $b$.

x=3(4+2)21x = \frac{3(4 + \sqrt{2})}{21}
x=4+27x = \frac{4 + \sqrt{2}}{7}
Comparing with a+b7\frac{a + \sqrt{b}}{7}, we have a=4a = 4 and b=2b = 2.

Answer

a=4a = 4, b=2b = 2

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