So I am trying to figure out the angle of a space motion vector with its radial velocity vector. I have to sample equations, but despite plugging in the numbers I am not getting the same answers.

So I have:

tan-1((4.74d(u")/(vr))

With:

d = 5.14 pc

u" = 0.66092"

vr = -26.3km s-1

so:

tan-1((4.74x5.14(0.66092)/-26.3)

= 1.1779

But the answer is supposed to -31.5

I tried convering parsecs and kilometers to meters, but still didn't get the right answer.

What am I missing?

Also, I am not entirely sure what the 4.74 number is, I can't find it in my text book.

Thankyou in advance!