Question

Determine the angles made by the vector v = (67)i + (-15)j with the positive x- and y-axes. write the unit vector n in the direction of v

Answer 1

Consider the picture attached.

From right triangle trigonometry: 

tan(α)=(opposite side)/(adjacent side)=15/67=0.2239

using a scientific calculator we find that arctan(0.2239)=12.62°

thus α=12.62°, is the angle that the vector makes with the positive x-axis.

The angle made with the + y-axis is 12.62°+90°=102.62°.



The length of the vector v can be determined using the Pythagorean theorem:

$|v|= \sqrt{ 67^{2} + 15^{2} }= \sqrt{4489+225}= \sqrt{4714}=68.8$


Thus, to make v a unit vector, without changing its direction, we need to divide v by |v|=68.8. 

This means that the x and y components will also be divided by 68.8, by proportionality.

So, the unit vector in the direction of v is:

(67/68.8)i + (-15/68.8)j=0.97 i + (- 0.22)j


Answer: 12.62°;  102.62°;  0.97 i + (- 0.22)j