Derivatives on your Ti-89
- You must have your calculator in radian mode when doing a derivative or indefinite (no bounds) integral to always get the correct answer. Why? It is a design flaw in my opinion.
- See the Trigonometry section to change the radian/degree mode.
- to perform a derivative, click 2nd->"8"
Entering in a Derivative
- Then enter in your equation using parenthesis making sure to put a multiplication sign between all the terms you want to multiply (even when using parenthesis, it doesn't infer what you are multiplying that well).
- Before closing off the final parenthesis, put in a comma, then put in the variable you want to derivate, then close the parenthesis [ie; if your equation is 0.5x^2; it should look like d(0.5x^2,x) your answer should be x]
- To do a multiple derivative (ie: 3rd derivative) enter it in the same as above but before closing the final parenthesis enter another comma then the number of derivatives you want it to do, then close the parenthesis. So to do a 3rd derivative of the above equation enter d(0.5x^2,x,3), you should get 0 for the answer, which makes sense.
- The picture to the left shows 3 things. On the bottom left it shows (highlighted) what it looks like to enter in an equation to derivate. Above that, it shows what the equation would look like on paper. Once the person hit "enter" it showed that answer on the right. Notice the calculator is in Radian mode (RAD AUTO) on the bottom of the screen.
- If you know what the value of the variable should be, after the closed parenthesis at the end press the | button (left side of the calculator) then type your "variable"="whatever number". ie: d(0.5x^2,x)|x=3 you should get 3 as your answer.
Common Problems
If this was really easy, everyone would use it! The truth is it can be tough to get a right answer every time, but below is all you need to know to solve your problems
- If it gives you a "Too few arguments", or "missing )" error , make sure all your parenthesis are closed and you have enough parenthesis. Also make sure your comma's are in the right place.
- If it still doesn't work correctly, make sure you have multiplication signs between the terms you want to multiply, even if you're using parenthesis to infer a multiplication.
- If it gives you an answer, but it looks wrong make sure you're in radian mode for a derivative or indefinite integral.
- If all else fails, click 2nd->6->F1-> scroll down to "All Memory" and hit enter. Or better yet to not get rid of your games and programs; 2nd-> F6 -> enter. (clear a-z) If you have accidentally assigned a value to a variable that your using, it will give you the wrong answer. Clearing the memory in either of these ways will fix this. For a more detailed overview of this point see calcblog's approach.
- After you enter in your equation and hit enter, look over the "handwritten" version of what you entered (see 4th bullet by picture) to make sure the calculator understands what you meant.
More Help
You might also want to check out Calcblog on derivatives (opens in a new window)
also check out youtube video's on the subject
also check out youtube video's on the subject