How to Graph a Web Plot on the TI-84 Plus

Web plots are a really interesting representation of the behavior of a recursive sequence, and you can use the TI-84 Plus to graph web plots. Web plots actually look a little like spider webs. Following are a few ground rules when working with web plots:

  • Sequence must be recursive: The sequence is required to have one level of recursion u(n–1); using u(n–2) is not allowed.

  • Sequence cannot reference n directly.

  • Sequence cannot reference any defined sequence except itself.

Here, you use the recursive sequence, an = –1/2(an–1), where a1 = 8.

Here are the steps to enter and graph a web plot in your calculator:

  1. Press [2nd][ZOOM] to access the Format menu.

  2. Use the arrow keys to navigate your cursor to Web in the top row and press [ENTER].

  3. Press [Y=] to access the Y= editor.

  4. Enter the recursive formula for u(n).

    Use u(n–1) for the previous term.

  5. Enter u(nMin).

    Enter the initial term in the sequence as shown in the first screen.

    image0.jpg
  6. Press [ZOOM][6].

    If you aren't sure what the graph of the web plot will look like, a ZStandard graphing window is a good place to start, as shown in the second screen.

    The line graphed at y = x is not part of the web plot; it is called the reference line.

  7. Press [TRACE] and press the right-arrow key repeatedly to draw the web.

    See the third screen. The web plot helps you see that this sequence converges.

    To clear a webplot, press [2nd][PRGM][ENTER].

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