The TI89 is pretty smart when it comes to approximation. If you enter just about any trigonometric function for calculation, it’ll return the exact value. On the home screen, none of the option menus have the exact( function, and to get to it, you need to use 2nd 5 (math) and scroll left. That’s great and all for exact numeric representations, but what if you didn’t want that? Approximations are useful too.
Let’s say you want the approximation of sin(43.3). Just running that command through the home screen without changing any settings will return the same thing, sin(43.3). While there is an exact( function, there is no approx( counterpart. That’s annoying.
To get the TI89 to return an approxmiation, it’s easy. First, enter the equation (sin(43.3) in our example) but don’t press enter yet. Instead, hit the star key. You’ll notice the star appears to the right of the main-keyword on the bottom of the screen. That means it worked right. You’ll also notice by looking at the enter key that there is a special star key function: approximate. The squiggly equals sign means approximate, and that’s what the TI89 will do as soon as you hit enter now. Do it this way, sin(43.3) returns -.630578.
There is more however. If you know for sure that you’ll be doing many approximations, you can set the TI89 to default to it. From the home screen, press the Mode key. Then go to page 2 using F2. Scroll down until Exact/Appox is selected. Press the right arrow to enter the toggle menu. The toggle menu allows auto, approx and exact. You can select the setting best for you.
Happy approximating!