# [SOLVED]311.1.3.2 u+v and u-2v and tikx?

#### karush

##### Well-known member
$\tiny{311.1.3.2}$
Compute $u+v$ and $u-2v$
$u=\left[ \begin{array}{rr} 3\\2 \end{array}\right], v=\left[ \begin{array}{rr}2\\-1 \end{array}\right] \quad u+v=\left[\begin{array}{rr}3+2\\2-1 \end{array}\right]= \left[\begin{array}{rr}5\\4 \end{array}\right] \quad u-2v=\left[\begin{array}{rr}3-2(2)\\2-2(-1) \end{array}\right] =\left[\begin{array}{rr}1\\0 \end{array}\right]$

ok I think this is correct typos maybe, but the next question is

Display the vectors using arrows on an xy-graph
$u,v, -v, -2v, u+v, u-v,$ and $u-2v$

I was going to try this with tikx but was looking for an example to follow since we use arrows

also is these vectors $\mathbb{R}^2$

Mahalo

#### skeeter

##### Well-known member
MHB Math Helper
$\tiny{311.1.3.2}$
Compute $u+v$ and $u-2v$
$u=\left[ \begin{array}{rr} 3\\2 \end{array}\right], v=\left[ \begin{array}{rr}2\\-1 \end{array}\right] \quad u+v=\left[\begin{array}{rr}3+2\\2-1 \end{array}\right]= \left[\begin{array}{rr}5\\4 \end{array}\right] \quad u-2v=\left[\begin{array}{rr}3-2(2)\\2-2(-1) \end{array}\right] =\left[\begin{array}{rr}1\\0 \end{array}\right]$

ok I think this is correct typos maybe, but the next question is

Display the vectors using arrows on an xy-graph
$u,v, -v, -2v, u+v, u-v,$ and $u-2v$

I was going to try this with tikx but was looking for an example to follow since we use arrows

also is these vectors $\mathbb{R}^2$

Mahalo
uhh ...

$u+v = \begin{bmatrix} 5\\ 1 \end{bmatrix}$

$u-2v = \begin{bmatrix} -1\\ 4 \end{bmatrix}$

try again ...

• karush and topsquark

#### Country Boy

##### Well-known member
MHB Math Helper
I am hoping that you know, perfectly well, that 2- 1= 1, not 4, and, although it is slightly more complicated, that 2- 2(-1)= 4. not 0.

• karush and topsquark

#### karush

##### Well-known member
$u=\left[ \begin{array}{rr} 3\\2 \end{array}\right], v=\left[ \begin{array}{rr}2\\-1 \end{array}\right] \quad u+v=\left[\begin{array}{rr}3+2\\2-1 \end{array}\right]= \left[\begin{array}{rr}5\\1 \end{array}\right] \quad u-2v=\left[\begin{array}{rr}3-2(2)\\2-2(-1) \end{array}\right] =\left[\begin{array}{rr}-1\\4 \end{array}\right]$

#### skeeter

##### Well-known member
MHB Math Helper
$u=\left[ \begin{array}{rr} 3\\2 \end{array}\right], v=\left[ \begin{array}{rr}2\\-1 \end{array}\right] \quad u+v=\left[\begin{array}{rr}3+2\\2-1 \end{array}\right]= \left[\begin{array}{rr}5\\1 \end{array}\right] \quad u-2v=\left[\begin{array}{rr}3-2(2)\\2-2(-1) \end{array}\right] =\left[\begin{array}{rr}-1\\4 \end{array}\right]$
So ... what now?

• karush

#### topsquark

##### Well-known member
MHB Math Helper
• karush

#### karush

##### Well-known member
how do you write a vector in tikz

• topsquark

MHB Math Helper

#### Klaas van Aarsen

##### MHB Seeker
Staff member
how do you write a vector in tikz
The following latex code does the job:
LaTeX:
\begin{tikzpicture}
\draw[->] (0,0) -- (3,2);
\end{tikzpicture}
\begin{tikzpicture}
\draw[->] (0,0) -- (3,2);
\end{tikzpicture}

A prettier version with some embellishments is:
LaTeX:
\begin{tikzpicture}
\coordinate[label=right:$\mathbf u$] (u) at (3,2);
\draw[-latex, thick] (0,0) -- node[above left] {$\vec u$} (u);
\end{tikzpicture}
\begin{tikzpicture}
\coordinate[label=right:$\mathbf u$] (u) at (3,2);
\draw[-latex, thick] (0,0) -- node[above left] {$\vec u$} (u);
\end{tikzpicture}

• karush and skeeter

Last edited: