Final answer:
When a point (a, b) is rotated 270° counterclockwise about the origin, the new coordinates become (b, -a), so the correct algebraic representation is D) (b, -a).
Step-by-step explanation:
The question asks for the algebraic representation of a point after a triangle is rotated 270° counterclockwise about the origin. When we rotate a point (a, b) 270° counterclockwise, the new coordinates become (b, -a). This is because a 270° counterclockwise rotation is equivalent to a 90° clockwise rotation, which switches the x and y coordinates and changes the sign of the new x-coordinate.
Therefore, the correct answer is D) (b, -a).