NSW Y12 Maths - Extension 1 Vectors Vectors in Component Form

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Vectors in Component Form Theory

The unit vector in the direction $\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a} $ is denoted $\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{\hat{a}}$ where $\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{\hat{a}}$ \(=\dfrac{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a} }{|\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a} |}\).\\  The component form of the vector $\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a} $ is $\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a} $\(=x i+y j\) which is equivalent to the column vector \(a=\left(\begin{array}{l}x \\ y\end{array}\right)\)\\  The magnitude of the vector $\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a} $\(=x i+y i\) is \(|\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}|=\sqrt{x^2+y^2}\)  Addition of vectors in component form if \(\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}=x_1 i+y_1 j\) and \(\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{b}=x_2 i+y_2 j\) then \(\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}+\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{b}=\left(x_1+x_2\right) u+\left(y_1+y_2\right) j\)\\  Subtraction of vectors in component form if \(\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}=x_1 i+y_1 j\) and \(\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{b}=x_2 i+y_2 j\) then \(\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}-\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{b}=\left(x_1-x_2\right) i+\left(y_1-y_2\right) j\)\\  Scalar multiplication of vectors in component form if \(a=x i+y j\) then \(k a=k x i+k y j\)  \begin{multicols}{2} \textbf{Relative position vectors}  \begin{center} \resizebox{0.3\textwidth}{!}{ \begin{tikzpicture} \draw[step=1cm, line width=0.2mm, black!40!white] (-5,-5) grid (5,5); \draw [draw=black] (-5,-5) rectangle (5,5); \draw[latex-latex,line width=0.5mm] (-5.5,0) -- (5.5,0) node[right]{\Large\(x\)}; \draw[latex-latex,line width=0.5mm] (0,-5.5) -- (0,5.5)node[above]{\Large\(y\)}; \foreach \x in {-5,-4,-3,-2,-1,1,2,3,4,5} \draw[thin] (\x,3pt )--(\x, -3pt ) node[anchor=north]{\Large\(\x\)}; \foreach \y in {-5,-4,-3,-2,-1,1,2,3,4,5} \draw[thin] (3pt, \y )--(-3pt, \y) node[anchor=east]{\Large\(\y\)}; \coordinate [label=below left:\Large$\mathbf{O}$   ] (O) at (0,0);   \coordinate [   label=above:\Large$\mathbf{A}$   ] (A) at (2,3);   \coordinate [   label=below:\Large$\mathbf{B}$   ] (B) at (3,-2);      \draw[line width=2pt]    (O)--(A)--(B)--cycle;  \path[decoration={markings, mark=at position 1 with {\arrow{latex[scale=4.5]}}}, postaction=decorate,line width=3pt] (O)--(A);  \path[decoration={markings, mark=at position 1 with {\arrow{latex[scale=4.5]}}}, postaction=decorate,line width=3pt] (O)--(B);   \path[decoration={markings, mark=at position 1 with {\arrow{latex[scale=4.5]}}}, postaction=decorate,line width=3pt] (B)--(A); \end{tikzpicture} } %\includegraphics[width=0.3\textwidth]{13ef2623-6326-470b-85f2-84fd73b74083} \end{center}  \columnbreak The position vector of A relative to \(B\) is \(\overrightarrow{A B}\)\\  $\begin{aligned} & \overrightarrow{A B}=\overrightarrow{A O}+\overrightarrow{O B} \\ & \overrightarrow{O A}=2 i+3j, \overrightarrow{O B}=3 i-2 j \\ & \therefore \overrightarrow{A B}=-\overrightarrow{O A}+\overrightarrow{O B} \\ &=-2i-3j+3i-2j \\ &=i-5j \end{aligned}$\\  \end{multicols}  \textbf{Parallel vectors}\\  If \(\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{b}=k \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}\) then $\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{b}$ is parallel to \(\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}\).\\  Unit vectors in component form  $\begin{aligned} \hat{a} & =\dfrac{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}}{|\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}|} \\ \text { If } \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a} & =x i+y j \\ \text { then } \hat{a} & =\dfrac{x i+y j}{\sqrt{x^2+y^2}} \\ \text { OR } \hat{a} & =\dfrac{1}{\sqrt{x^2+y^2}}(x i+y j) \end{aligned}$\\ \textbf{Example 1}\\ For the position vectors \(\overrightarrow{O M}=3 i-6 j\) and \(\overrightarrow{O N}=-3 i+6j\),  what is the value of \(|\overrightarrow{M N}|\)\\  \textbf{Example 1 solution}\\ $\begin{aligned} \overrightarrow{M N} & =\overrightarrow{M O}+\overrightarrow{O N} \\ & =-(3 i-6 i)+(-3 i+6 j) \\ & =-6 i+12 j \\ |\overrightarrow{M N}| & =\sqrt{36+144} \\ & =6 \sqrt{5} . \end{aligned}$\\  \textbf{Example 2}\\ What is the unit vector in the direction \(\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a} =-3 i+4 j\)?\\  \textbf{Example 2 solution}\\ $\begin{aligned} & \hat{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}}=-\frac{3 i+4 j}{\sqrt{9+16}} \\ & \hat{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}}=\frac{1}{5}(-3 i+4 j) \end{aligned}$\\  \textbf{Example 3}\\ Given \(\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}=-10 i+23 j\) and \(\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{b}=5 i+18 j\) find the value of \(k\) so the vector \(k \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}+4 \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{b}\) is parallel to the \(y\)-axis.\\  \textbf{Example 3 solution}\\ $\begin{aligned}  k \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{a}+4 \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{b}&=k(-10 i+23 j)+4(5 i+18 j) \\ & =-10 k i+23 k j+20 i+72 j \\ & =(20-10 k) i+(72+23 k) j \\ \text { Parallel to } y \text {-axis } &\therefore 20-10 k=0 \\ & \therefore k=2 \end{aligned}$\\

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