Hello, I'm very relieved to have found this website!!

I am trying to do the following question:-

I have drawn this:-A rectangle OBCA in the xy-plane has vertices O(0,0), B(-3,4), C(5,10) and A(8.6).

Determine the magnitude and direction of the following vectors

1) OB

2) OD

I'm attempting part 1 and have the magnitude (which is 5) but am unsure how to work out the magnitude.

I have the answer (it is 126.87 degrees), but this is confusing me as the triangle looks to be a right angled triangle, and so 90 + 126.87 is way over 180 degrees, so I'm clearly not working this out correctly.

I've memorised SOC-CAH-TOA.

Many thanks!!!