Question

triangle has vertices at A (1,3), B(4,2), and C (3,8). Which transformation would produce an image with vertices A'(3, -1), B(2,-4), C' (8, -3)

Answer 1

You would have a 90 degree clockwise rotation. 

Rules:

90 Clockwise: Flip, change right sign / y, -x
90 Counter CW: Flip, change left sign. / -y, x

Answer 2

If the triangle is moved 90°C to the left.