OCR C1 2015 June — Question 1 3 marks

Exam BoardOCR
ModuleC1 (Core Mathematics 1)
Year2015
SessionJune
Marks3
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicIndices and Surds
TypeRationalize denominator simple
DifficultyEasy -1.2 This is a straightforward application of rationalizing the denominator by multiplying by the conjugate. It requires only one standard technique (multiply by (√3+1)/(√3+1)) and simple arithmetic to reach the form a√3+b. This is a routine C1 exercise with no problem-solving element.
Spec1.02b Surds: manipulation and rationalising denominators

1 Express \(\frac { 8 } { \sqrt { 3 } - 1 }\) in the form \(a \sqrt { 3 } + b\), where \(a\) and \(b\) are integers.

Question 1:
AnswerMarks Guidance
AnswerMarks Guidance
\(\frac{8}{\sqrt{3}-1} \times \frac{\sqrt{3}+1}{\sqrt{3}+1}\)M1 Multiply top and bottom by \(\sqrt{3}+1\) or \(-\sqrt{3}-1\); evidence of multiplying out needed
\(\frac{8\sqrt{3}+8}{3-1}\)A1 Either numerator or denominator correct
\(4\sqrt{3}+4\)A1 Final answer cao
Alternative: M1 Correct method to solve simultaneous equations formed from equating expression to \(a\sqrt{3}+b\); A1 Either \(a\) or \(b\) correct; A1 Both correct
## Question 1:

| Answer | Marks | Guidance |
|--------|-------|----------|
| $\frac{8}{\sqrt{3}-1} \times \frac{\sqrt{3}+1}{\sqrt{3}+1}$ | M1 | Multiply top and bottom by $\sqrt{3}+1$ or $-\sqrt{3}-1$; evidence of multiplying out needed |
| $\frac{8\sqrt{3}+8}{3-1}$ | A1 | Either numerator or denominator correct |
| $4\sqrt{3}+4$ | A1 | Final answer **cao** |

**Alternative:** M1 Correct method to solve simultaneous equations formed from equating expression to $a\sqrt{3}+b$; A1 Either $a$ or $b$ correct; A1 Both correct

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1 Express $\frac { 8 } { \sqrt { 3 } - 1 }$ in the form $a \sqrt { 3 } + b$, where $a$ and $b$ are integers.

\hfill \mbox{\textit{OCR C1 2015 Q1 [3]}}