1. Finding the rotation in Radians

I am asked to move a triangle so that C is at the origin and CB lies along the positive x-axis.

The original vertices were A(7,5), B(5,1) and C(-4,2).

The translated vertices are A(11,3), B(9,-1) and C(0,0). Which is t:4,-2 (x+4, y-2).

Now, I'm onto the rotation part. How do I find the exact values of cosθ, sinθ and tanθ and hence write down a formal definition of rθ?

The perplexing part is that the question states that I don't need to work out the angle θ.
Perhaps a fresh pair of eyes on the question will help (please PM me if you'd like to read the Q in full).

If you can help me solve this, I will be most grateful.

2. Originally Posted by mezhopking
I am asked to move a triangle so that C is at the origin and CB lies along the positive x-axis.

The original vertices were A(7,5), B(5,1) and C(-4,2).

The translated vertices are A(11,3), B(9,-1) and C(0,0). Which is t:4,-2 (x+4, y-2).

Now, I'm onto the rotation part. How do I find the exact values of cosθ, sinθ and tanθ and hence write down a formal definition of rθ?

The perplexing part is that the question states that I don't need to work out the angle θ.
Perhaps a fresh pair of eyes on the question will help (please PM me if you'd like to read the Q in full).

If you can help me solve this, I will be most grateful.
$\displaystyle \tan(\theta)=\dfrac{-1}9$