4 keys to mastering dilations from the y-axis

Tricky tricky tricky…

Perhaps this little summary will help clear up the confusion about when to use the reciprocal and when not. Click on the link below to download your own copy to add to your summary notes. Be aware the ‘opposite’ is also readily tested: you might be told that a functions has been dilated by a factor of 3 from the y-axis, and you’ll need to know what to write/how to modify the equation. For the record – it needs to read as f(1/3x), i.e. write a 1/3 in the equation beside the x.

dilation_from_y

Click here to download your own printable version: Dilations from the y-axis.jpg (313 KB)

  • Steve Horn

    Good stuff Freda! Thanks
    In describing translations such as y = f(4-2x) for example, We (my class) refer to ‘x’ as ‘evil x’ because it can easily trap the kids in many ways.
    Always look for a common factor, especially negative ones!
    so y = f(-2(x-2))
    We have a dilation of 1/2 a from the y- axis, a reflection about the y-axis and a translation 2 in the positive x direction.
    I thinks this is right? Coffee just kicking in ๐Ÿ™‚
    This is my first go at Methods 3/4 and I’m on my own, so I really love your posts and site.
    Cheers
    Steve

  • Great to hear Steve. Thanks for letting me know – glad you’re finding them helpful! My kids love this because they always get confused about when to use the reciprocal. You’re right about the transformations. Tricky when you’re dealing with an already transformed graph, such as y=(x-4)^3. Order is so important!