How can I have a negative angle?

[joe215]

1. Homework Statement

Find the vector with the components: Ax=3.2 Ay= -5.15

2. The attempt at a solution

-5.15^2 + 3.2^2= 36.76
sq root of 36.76= 6.06
So, the magnitude is 6.06. Now for the direction...

Tan theta=-5.15/3.2
ArcTan(-1.6)= -57.99 degrees

How can I have a negative angle?

Thanks so much!

 

[HallsofIvy]

` What does the angle mean? If you were to actually draw that vector on an xy-coordinate system, you would draw it making that angle with the "positive x-axis"-to the right- measuring the angle "counter-clockwise" of course.. A negative angle would mean measuring clockwise- down rather than up. If you look at the y components, you will see that the reason the angle is negative is because the y component is negative- the vector points downward.