Is the relation (-1, 1), (-2, 3), (-3, 5), (-4, 7), (-5, 9) a function?

None of the x values repeat, so each x input leads to exactly one y output.

If you had two points such as (-1,1) and (-1,2), then the input x = -1 leading to multiple outputs y = 1 and y = 2 would rule it out of being a function.

Visually, plotting each point given shows that it is impossible to draw a single vertical line through more than one point, which shows the relation passes the vertical line test.