Back to Orthogonal Projection Into a Line

Exercise 4

Avg difficulty 3.0

Definition 1.1 uses two vectors s⃗\vec{s} and v⃗\vec{v}. Consider the transformation of R2\mathbb{R}^{2} resulting from fixing

s⃗=(31)\vec{s}=\begin{pmatrix}3\\ 1\end{pmatrix}

and projecting v⃗\vec{v} into the line that is the span of s⃗\vec{s}. Apply it to these vectors.

  • (a)  (12)\begin{pmatrix}1\\ 2\end{pmatrix}     (b)  (04)\begin{pmatrix}0\\ 4\end{pmatrix}

Show that in general the projection transformation is this.

(x1x2)↦((9x1+3x2)/10(3x1+x2)/10)\begin{pmatrix}x_{1}\\ x_{2}\end{pmatrix}\mapsto\begin{pmatrix}(9x_{1}+3x_{2})/10\\ (3x_{1}+x_{2})/10\end{pmatrix}

Express the action of this transformation with a matrix.

Hefferon, Linear Algebra, Maps Between Spaces, Orthogonal Projection Into a Line, Exercise 4

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Adapted from Linear Algebra © 2016 Jim Hefferon. Licensed under CC BY-SA 3.0 US. Source: Linear Algebra. Imported at revision df2262e.