Question

Which of the following graphs represents a one-to-one function?

Answer 1

Answer with explanation:

We know that a function is one-to-one if each of x is mapped to a unique element i.e. no two 'x' are mapped to the same-element i.e. it passes the horizontal line test.

(i.e. any line passing through the co-domain and parallel to x-axis should intersect the graph atmost once)

The graph that passes such test and is one-to-one is attached to the answer.(The graph with discrete points)

while in other graphs the horizontal line test is ruled out.

(as the line touches the curve at more than one point)

Answer 2

Graph A is a one to one function No two x's go to the same y and no two y's go to the same x.

Another way to think of it. It must pass both the horizontal and vertical line tests.