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What is the direction, in degrees and to 2 decimal places, for the vector whose column form is \[ \begin{pmatrix} a & b \end{pmatrix} \] where $a = 19$ and $b = -5$? Do not give any units in your answer. Your answer must be between $-90°$ and $270°$.

I got the answer as $-75.26°$. I used

\[ \arctan \frac{19}{-5}\]

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Is this a question? It also sounds like a homework issue. –  kcrisman Sep 11 '12 at 15:08
    
it is @kcrisman ! ;) –  JackyBoi Sep 11 '12 at 15:20

1 Answer 1

up vote 1 down vote accepted

Draw a picture, perhaps more or less to scale. Note that the slope is "rise" divided by "run". Or, in symbols, the slope is the change in $y$ divided by the change in $x$.

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haha i did and i got the answer so just verifying if it is correct tks –  JackyBoi Sep 11 '12 at 15:21
    
@JackyBoi: Do the picture as I suggested. Your answer is not correct. Picture will show that. Your expression is upside down. –  André Nicolas Sep 11 '12 at 15:32
    
any example? cause my textbook doesnot have such slope and rise concept perhaps i will learn.. tks –  JackyBoi Sep 11 '12 at 15:34
    
@JackyBoi: Change the problem slightly to $a=19$, $b=5$. The slope is $\frac{5}{19}$: the tangent of the angle is opposite divided by adjacent. For your problem, you will want $\arctan(-5/19)$. –  André Nicolas Sep 11 '12 at 15:40
    
so -14.74? is that the answer? –  JackyBoi Sep 12 '12 at 0:28

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