Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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

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

share|cite|improve this question
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
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 $x$.

share|cite|improve this answer
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

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.