OCR FP1 2007 June — Question 2 5 marks

Exam BoardOCR
ModuleFP1 (Further Pure Mathematics 1)
Year2007
SessionJune
Marks5
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicProof by induction
TypeProve summation formula
DifficultyStandard +0.3 This is a standard textbook induction proof with a given formula to verify. The algebraic manipulation in the inductive step is straightforward—factoring n²(n+1)² and showing (n+1)³ fits the pattern. While it's Further Maths content, it's one of the most routine induction questions possible, requiring only mechanical execution of the standard method with minimal algebraic challenge.
Spec4.01a Mathematical induction: construct proofs

2 Prove by induction that, for \(n \geqslant 1 , \sum _ { r = 1 } ^ { n } r ^ { 3 } = \frac { 1 } { 4 } n ^ { 2 } ( n + 1 ) ^ { 2 }\).

AnswerMarks Guidance
\((1^3 =) \frac{1}{4} \times 1^2 \times 2^2\)B1 Show result true for \(n = 1\).
\(\frac{1}{4}n^2(n+1)^2 + (n+1)^3\)M1 M1(indep) Add next term to given sum formula. Attempt to factorise and simplify.
\(\frac{1}{4}(n+1)^2(n+2)^2\)A1 Correct expression obtained convincingly.
5Specific statement of induction conclusion.
Total: 5 marks
$(1^3 =) \frac{1}{4} \times 1^2 \times 2^2$ | B1 | Show result true for $n = 1$. |

$\frac{1}{4}n^2(n+1)^2 + (n+1)^3$ | M1 M1(indep) | Add next term to given sum formula. Attempt to factorise and simplify. |

$\frac{1}{4}(n+1)^2(n+2)^2$ | A1 | Correct expression obtained convincingly. |

| | 5 | Specific statement of induction conclusion. |

**Total: 5 marks**
2 Prove by induction that, for $n \geqslant 1 , \sum _ { r = 1 } ^ { n } r ^ { 3 } = \frac { 1 } { 4 } n ^ { 2 } ( n + 1 ) ^ { 2 }$.

\hfill \mbox{\textit{OCR FP1 2007 Q2 [5]}}