Question

Identify the coordinates of (3, –9) after a rotation of 180° about the origin.

Answer 1

Answer: (-3,9)

When we rotate 180 degrees about the origin, the rule is (x,y) --> (-x,-y). The coordinate signs have swapped. If x is negative, then x turns positive, or vice versa. The same applies for y as well.
x = 3 becomes -x = -3
y = -9 becomes -y = -(-9) = 9