20 Most Recent Texas Instruments TI-83 Plus Silver Edition Calculator Questions & Answers

The manual can be downloaded from here: http://college.cengage.com/mathematics/latorre/calculus_concepts/4e/assets/students/gcp/latorre_4e_grcalcguide.pdf First instance of discussion is on page 1.

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Your stat plots are on, and may not be filled out/ correctly filled out.
go to [Y=] and go up to the stat plots ([Plot 1], [Plot 2], [Plot 3] ) and turn off the ones that are "ON" ( highlighed black w/ white text.) and press [ENTER] on the ones that are on and the problem is no more.

Use the ^ key, located just above the divide key. For example, to raise 2 to the fifth power, press 2 ^ 5 ENTER.

I admit that I do not quite understand what you want to do. The Zoom function allows the user to Zoom In ( see a smaller part of the graph in more detail ) or Zoom Out (to view more of the graph in less details) That applies to any graph that is displayed
As to the square root function, if you enclose the argument (expression) in parentheses making sure that you close the right one ) , everything inside the () will be part of the argument.

It means there was a problem with your syntax which means you typed something incorrect. (like 8+*/8, which makes no sense and cannot be computed.)