Rationalised, $\dfrac{5+\sqrt2}{\sqrt6-\sqrt2}$ simplifies to:
A$\dfrac{5\sqrt6+5\sqrt2+2\sqrt3+2}{8}$
B$\dfrac{5\sqrt6+5\sqrt2+2\sqrt3+2}{4}$
C$\dfrac{5\sqrt6-5\sqrt2+2\sqrt3-2}{4}$
D$\dfrac{30+4\sqrt3+2\sqrt2}{4}$
Answer & Solution
Correct answer: B. $\dfrac{5\sqrt6+5\sqrt2+2\sqrt3+2}{4}$
1. Multiply numerator and denominator by the conjugate $\sqrt6+\sqrt2$.
2. The denominator becomes $(\sqrt6)^2-(\sqrt2)^2=6-2=4$.
3. Expand the numerator: $(5+\sqrt2)(\sqrt6+\sqrt2)=5\sqrt6+5\sqrt2+\sqrt{12}+2$.
4. Simplify $\sqrt{12}=2\sqrt3$.
5. So the result is $\dfrac{5\sqrt6+5\sqrt2+2\sqrt3+2}{4}$. Writing the numerator as $30-4$ multiplies the terms instead of expanding them, which the report records as a common slip.
_Source: NECTA CSEE 2022 Basic Mathematics 041, Question 2: Exponents, Radicals and Logarithms_
Keep practising Exponents, Radicals and Logarithms
Browse all Exponents, Radicals and Logarithms questions for CSEE (Form 4), or explore more Basic Mathematics topics.
Related questions
Spot the intruderComplete the surd workMatch the log law to its formSolve an exponential equationFault the wrong rationalising factorsThe rationalising factor needed to simplify $\dfrac{5+ qrt2}{ qrt6- qrt2}$ is:Simplified, $\log_a qrt{a}+\log_a(a^2)$ equals:Solving $8^{x-1}=16$ using the laws of exponents gives $x$ equal to: