A transformation rotates about the origin by an angle of $45^\circ$ counter-clockwise, then dilates (with center at the origin) by a factor of $\sqrt{2}.$ Find the matrix for this transformation.

Respuesta :

The matrix for the combined rotation transformation of 45° and dilation

of [tex]\sqrt{2}[/tex] gives the matrix for the transformation as follows;

[tex]Matrix \ for \ the \ rotation \ and \ dilation \ is;\left[\begin{array}{cc}1 &-1\\1&1\end{array}\right][/tex]

How can the transformation matrix be found?

The angle by which the transformation rotates about the origin = 45°

The dilation following the rotation = A factor of √2

Required:

The matrix for the transformation

Solution:

The dilation matrix for a scale factor of [tex]\mathbf{\sqrt{2}}[/tex] is presented as follows;

[tex]\mathbf{\left[\begin{array}{cc}\sqrt{2} &0\\0&\sqrt{2} \end{array}\right]}[/tex]

[tex]The \ transformation \ for \ a \ rotation \ of \ 45^{\circ} \ is; \left[\begin{array}{cc}cos(45^{\circ})&-sin(45^{\circ})\\sin(45^{\circ})&cos(45^{\circ})\end{array}\right][/tex]

[tex]\left[\begin{array}{cc}cos(45^{\circ})&-sin(45^{\circ})\\&\\sin(45^{\circ})&cos(45^{\circ})\end{array}\right] = \mathbf{\left[\begin{array}{cc}\dfrac{\sqrt{2} }{2} &-\dfrac{\sqrt{2} }{2} \\&\\ \dfrac{\sqrt{2} }{2} &\dfrac{\sqrt{2} }{2} \end{array}\right]}[/tex]

Which gives;

[tex]\left[\begin{array}{cc}\dfrac{\sqrt{2} }{2} &-\dfrac{\sqrt{2} }{2} \\&\\ \dfrac{\sqrt{2} }{2} &\dfrac{\sqrt{2} }{2} \end{array}\right] \times \left[\begin{array}{cc}\sqrt{2} &0\\0&\sqrt{2} \end{array}\right] = \left[\begin{array}{cc}\dfrac{\sqrt{2} \times \sqrt{2} }{2} &-\dfrac{\sqrt{2} \times \sqrt{2} }{2} \\&\\ \dfrac{\sqrt{2} \times \sqrt{2} }{2} &\dfrac{\sqrt{2} \times \sqrt{2} }{2} \end{array}\right] = \left[\begin{array}{cc}1 &-1\\1&1\end{array}\right][/tex]

The required matrix for the transformation is therefore;

  • [tex]\left[\begin{array}{cc}1 &-1\\1&1\end{array}\right][/tex]

Learn more about other forms of transformation matrices here:

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