![\"\"](\"/userfiles/image/steps_images/step1.JPG\")
The function is ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=07215150608e2db7776b0e23cef956af.png\")
.
Horizontal line test:
\A function is one-to-one if and only if no horizontal line intersects its graph more than once.
\That is, any horizontal line in the graph must cross the curve at one point only.
\\
![\"\"](\"/userfiles/390-10.gif\")
Observe the graph :
\Draw the horizontal line ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=c3f40df3b6ee26c4ed5b179d6afd8b20.png\")
, this 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.