Answer
a) $(a,-b)$
b) $(-a,b)$
c) $(-a,-b)$
Work Step by Step
a) $(a,-b)$ because we flip the y-coordinate when reflecting across the x-axis
b) $(-a,b)$ because we flip the x-coordinate when reflecting across the y-axis
c) $(-a,-b)$ because we flip both the x and y-coordinate when reflecting across the origin