![\"\"](\"/userfiles/image/steps_images/step1.JPG\")
Horizontal line test :
\A function is one-to-one if and only if no horizontal line intersects its graph more than once.
\Draw a horizontal line.
\![\"\"](\"/userfiles/390-7.gif\")
Observe the graph :
\The horizontal line does not touch the graph more than once.
\The function is a one-to-one, because it passes the horizontal line test.
\![\"\"](\"/userfiles/image/steps_images/solution.JPG\")
The function is an one-to-one.