Find the angle between the vectors u and v if

Question

u = (-1,4)
v = (3,-4)

a. 155.93
b. 158.58
c. 158.13
d. 155.24
e. 157.17

Answer 1

just plug in your numbers:

cosθ =
u•v
-----------------------
|u| |u|

Answer 2

I've tried this and got - 0.9216353751380653

can you help me any further please?