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Linear transformationsAQA A-Level Further Maths: Flashcards

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Where do the columns of a transformation matrix come from?

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Where do the columns of a transformation matrix come from?
They are the images of the unit vectors (1,0)(1,0) and (0,1)(0,1) (and (0,0,1)(0,0,1) in 3D).
Matrix for a rotation of θ\theta anticlockwise about the origin?
(cos⁡θ−sin⁡θsin⁡θcos⁡θ)\begin{pmatrix}\cos\theta&-\sin\theta\\ \sin\theta&\cos\theta\end{pmatrix}
Matrix for reflection in y=xy=x?
(0110)\begin{pmatrix}0&1\\1&0\end{pmatrix}
Matrix for reflection in y=−xy=-x?
(0−1−10)\begin{pmatrix}0&-1\\-1&0\end{pmatrix}
Matrix for an enlargement, scale factor kk, centre the origin?
(k00k)\begin{pmatrix}k&0\\0&k\end{pmatrix}
Matrix for a shear with the xx-axis invariant, sending (0,1)(0,1) to (λ,1)(\lambda,1)?
(1λ01)\begin{pmatrix}1&\lambda\\0&1\end{pmatrix}
Matrix of AA followed by BB?
BA\mathbf{B}\mathbf{A} (the first transformation is on the right).
Is the order of successive transformations important?
Yes: matrix multiplication is not commutative, so BA≠AB\mathbf{B}\mathbf{A}\neq\mathbf{A}\mathbf{B} in general.
Matrix for reflection in the plane x=0x=0?
(−100010001)\begin{pmatrix}-1&0&0\\0&1&0\\0&0&1\end{pmatrix}
Matrix for a rotation through θ\theta about the zz-axis?
(cos⁡θ−sin⁡θ0sin⁡θcos⁡θ0001)\begin{pmatrix}\cos\theta&-\sin\theta&0\\ \sin\theta&\cos\theta&0\\0&0&1\end{pmatrix}
Matrix for a rotation through θ\theta about the yy-axis?
(cos⁡θ0sin⁡θ010−sin⁡θ0cos⁡θ)\begin{pmatrix}\cos\theta&0&\sin\theta\\0&1&0\\-\sin\theta&0&\cos\theta\end{pmatrix}
Which direction is a positive rotation about a coordinate axis?
Anticlockwise when looking from the positive axis towards the origin (right-hand rule).

Exam questions on Linear transformations

  1. The matrix M=(0−110)\mathbf{M}=\begin{pmatrix}0&-1\\1&0\end{pmatrix} represents a transformation TT of the plane.
    The point PP is mapped by TT to (−4,5)(-4,5). Find the coordinates of PP.2 marks
  2. The unit square OABCOABC has vertices O(0,0)O(0,0), A(1,0)A(1,0), B(1,1)B(1,1) and C(0,1)C(0,1). It is transformed by the matrix N=(1201)\mathbf{N}=\begin{pmatrix}1&2\\0&1\end{pmatrix}.
    Describe fully the single transformation represented by N2\mathbf{N}^2.2 marks
  3. Transformation PP is a rotation through 90∘90^\circ clockwise about the origin, and transformation QQ is a reflection in the line y=xy=x.
    Find the single matrix that represents PP followed by QQ.3 marks
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).