12-

pls help

math

-
—

c

Step-by-step explanation:

Easiest way is drawing the vectors.

If you need a better reason you can get it through dot product.

Let X be the angle needed.

Dot product of two vectors is defined as

A •B = |A||B|cosX

where X is the angle between A and B

cosX=A•B/ |A||B|

=(-1×-9+1×0) / (√(-1^2+1^2)×√(-9^2))

=1/√2

So the answer is X=45°