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Interactive practice · Further Maths
Work through exam-style OCR Further Maths solutions one line at a time. At each step, choose the line you think comes next, some of the wrong options are exactly what you'd write after a slip earlier on. Press Mark to see which steps you got right and why the others are wrong. This is practice, not a study guide: do it actively.
Stuck on a step?
If the same kind of slip keeps costing you method and accuracy marks, a few focused sessions fix it fast. One-to-one online A-Level Maths and Further Maths tuition, matched to your exam board.
Every question below is fully interactive above: open it, build the solution line by line, and be marked against an authentic OCR-style mark scheme with per-line feedback. The stems are listed here in full.
\(|z|=\sqrt{(-2)^{2}+(-2\sqrt{3})^{2}}=\sqrt{4+12}=4\) (B1).
The acute angle to the real axis is \(\arctan\sqrt3=\tfrac{\pi}{3}\); both parts are negative so \(z\) is in the third quadrant (M1). Measuring clockwise, \(\arg z=-(\pi-\tfrac{\pi}{3})=-\tfrac{2\pi}{3}\) (A1).
\(|z|=4,\ \arg z=-\tfrac{2\pi}{3}\). Total: 3 marks.
By De Moivre, \(z^{4}=3^{4}\big(\cos(4\cdot\tfrac{\pi}{4})+i\sin(4\cdot\tfrac{\pi}{4})\big)\) (M1) \(=81(\cos\pi+i\sin\pi)\) (A1).
Since \(\cos\pi=-1\) and \(\sin\pi=0\):
\(z^{4}=-81\). (A1) Total: 3 marks.
\(AB=\begin{pmatrix}3&-1\\2&4\end{pmatrix}\begin{pmatrix}1&2\\5&-3\end{pmatrix}=\begin{pmatrix}3(1)+(-1)(5)&3(2)+(-1)(-3)\\2(1)+4(5)&2(2)+4(-3)\end{pmatrix}\) (M1 A1 top row, A1 bottom row).
\(AB=\begin{pmatrix}-2&9\\22&-8\end{pmatrix}\). Total: 3 marks.
\(\det M=(4)(5)-(3)(2)=14\) (B1); since it is non-zero, \(M\) is invertible.
Adjugate: swap the leading diagonal and negate the rest to get \(\begin{pmatrix}5&-3\\-2&4\end{pmatrix}\) (M1).
\(M^{-1}=\dfrac{1}{14}\begin{pmatrix}5&-3\\-2&4\end{pmatrix}\). (A1) Total: 3 marks.
For \(ax^{3}+bx^{2}+cx+d=0\): \(\alpha+\beta+\gamma=-\tfrac{b}{a}\), \(\sum\alpha\beta=\tfrac{c}{a}\), \(\alpha\beta\gamma=-\tfrac{d}{a}\).
Here \(a=3,\ b=4,\ c=-6,\ d=8\), so \(\alpha+\beta+\gamma=-\tfrac{4}{3}\) (B1), \(\alpha\beta+\beta\gamma+\gamma\alpha=\tfrac{-6}{3}=-2\) (B1), \(\alpha\beta\gamma=-\tfrac{8}{3}\) (B1).
\(\alpha+\beta+\gamma=-\tfrac{4}{3},\quad \sum\alpha\beta=-2,\quad \alpha\beta\gamma=-\tfrac{8}{3}\). Total: 3 marks.
Base case \(n=1\): LHS \(=1\), RHS \(=\tfrac14(1)^2(2)^2=1\) (B1).
Inductive step: assume \(\sum_{r=1}^{k}r^3=\tfrac14 k^2(k+1)^2\). Then \(\sum_{r=1}^{k+1}r^3=\tfrac14 k^2(k+1)^2+(k+1)^3\) (M1) \(=\tfrac14(k+1)^2\big[k^2+4(k+1)\big]\) (dM1).
\(k^2+4(k+1)=k^2+4k+4=(k+2)^2\) (A1), so \(\sum_{r=1}^{k+1}r^3=\tfrac14(k+1)^2(k+2)^2\), the formula with \(n=k+1\). True for \(n=1\), and \(P(k)\Rightarrow P(k+1)\), so true for all \(n\in\mathbb{Z}^{+}\) (A1).
\(\sum_{r=1}^{n} r^{3}=\tfrac{1}{4}n^{2}(n+1)^{2}\). Total: 6 marks.
\(\sum_{r=1}^{n}\tfrac{1}{r(r+2)}=\tfrac12\sum_{r=1}^{n}\big(\tfrac1r-\tfrac1{r+2}\big)=\tfrac12\big[(\tfrac11-\tfrac13)+(\tfrac12-\tfrac14)+\dots+(\tfrac1{n}-\tfrac1{n+2})\big]\) (M1).
The gap of 2 means survivors are \(+\tfrac11,+\tfrac12,-\tfrac1{n+1},-\tfrac1{n+2}\) (M1), giving \(\tfrac12\big(1+\tfrac12-\tfrac1{n+1}-\tfrac1{n+2}\big)\) (A1).
\(=\tfrac34-\tfrac{2n+3}{2(n+1)(n+2)}=\dfrac{n(3n+5)}{4(n+1)(n+2)}\) (A1).
\(\sum_{r=1}^{n}\dfrac{1}{r(r+2)}=\dfrac{n(3n+5)}{4(n+1)(n+2)}\). Total: 4 marks.
\(\cosh x=\tfrac{e^{x}+e^{-x}}{2}=\tfrac54\Rightarrow 2(e^{x}+e^{-x})=5\) (M1). Times \(e^{x}\): \(2e^{2x}-5e^{x}+2=0\) (M1).
\((2e^{x}-1)(e^{x}-2)=0\Rightarrow e^{x}=\tfrac12\ \text{or}\ 2\) (dM1). Both are positive, so \(x=\ln2\) (A1) and \(x=\ln\tfrac12=-\ln2\) (A1).
\(x=\pm\ln 2\). Total: 5 marks.
\(V=\pi\int_{0}^{4} y^{2}\,dx=\pi\int_{0}^{4} x\,dx\) (M1) \(=\pi\left[\tfrac{x^{2}}{2}\right]_{0}^{4}\) (A1) \(=\pi\left(\tfrac{16}{2}-0\right)\) (dM1).
\(V=8\pi\). (A1) Total: 4 marks.
\(\mathbf{a}\cdot\mathbf{b}=(2)(1)+(-1)(2)+(2)(2)=4\) (M1).
\(|\mathbf{a}|=\sqrt{4+1+4}=3\) and \(|\mathbf{b}|=\sqrt{1+4+4}=3\) (B1).
\(\cos\theta=\dfrac{\mathbf{a}\cdot\mathbf{b}}{|\mathbf{a}||\mathbf{b}|}=\dfrac{4}{(3)(3)}\) (M1) \(=\dfrac{4}{9}\) (A1), so \(\theta\approx63.6^{\circ}\) (acute).
\(\cos\theta=\tfrac{4}{9}\). Total: 4 marks.
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