Trigonometry question

Question

Find the approximate angle that the vector v=-2i+4j makes with the positive x-axis

Answer 1

To find the angle, use tangent inverse.

θ = tan^-1(4/2) [notice we are ignoring the negative sign on the "i" direction. We will account for that later.]

Plugging that into your calculator gives θ = 63.435° but the question asks the angle between the POSITIVE x-axis. So to find that, take 180° - θ or 116.565° This "adjustment, accounts for the negative "i" direction. There are many possibilities for angles from zero to 360° and calculators won't always take into account the exact location in that circle so you are required to put some thinking into the application of the trig ratios.

Hopefully that helps.