The ZTrig Command

Command Summary

Zooms to a trigonometry-friendly window.

Command Syntax

ZTrig

Press:

1. ZOOM to access the zoom menu.
2. 7 to select ZTrig, or use arrows and ENTER.

TI-83/84/+/SE

1 byte

The ZTrig command sets the screen to a special friendly window useful for trigonometric calculations. Unlike the ZDecimal and ZInteger commands, for which the distance between two pixels is a short decimal or integer, ZTrig sets the horizontal distance between two pixels to be π/24 (in Radian mode) or 7.5 (in Degree mode) . The specific changes ZTrig makes are:

• Xmin=-352.5° or -47/24πr
• Xmax=352.5° or 47/24πr
• Xscl=90° or π/2r
• Ymin=-4
• Ymax=4
• Yscl=1

Although this window is not quite square (and therefore, distances in the X and Y direction are not exactly equally proportioned), it is quite close, when in Radian mode. In a square window (such as the output of ZSquare), Ymax would have to be 31/24π, which is approximately 4.05789. As you can see, the value of 4 that ZTrig uses is not too far off.

In theory, ZTrig should be quite useful in graphing trigonometric functions, since the calculated points would fall exactly on important angles; for example, it would graph the asymptotes of Y=tan(X) correctly. This is actually only true when in Degree mode. In Radian mode, due to round-off error, the pixels far away from the origin do not exactly correspond to rational multiples of π. For example, the pixel which was supposed to correspond to π/2 actually has a value of .5000000001*π, which is enough to make this command mostly useless.

However, in G-T mode, the size that the graph takes up on the screen is different, and ZTrig uses the same values, unlike ZDecimal.

# Error Conditions

• ERR:INVALID occurs if this command is used outside a program (but not if the menu option is used, of course).