Question

Suppose xy > 0. Describe the points whose coordinates are solutions to the inequality.

Answer 1

all points in the 1st and 3rd quadrants (not including the x- and y-axes).

Explanation:

The product of positive numbers will be greater than 0, as will the product of two negative numbers. Both coordinates are positive in the first quadrant; both are negative in the third quadrant.

The quadrant boundaries, x=0, y=0, are excluded from the solution set.