![\"\"](\"/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/390-8(1).gif\")
Observe the graph :
\The function attains the value twice, around its maximum and minimum.
\The function is not one-to-one, because it violates the horizontal line test.
\![\"\"](\"/userfiles/image/steps_images/solution.JPG\")
The function is not one-to-one.