Hi everyone,

Is anyone familiar with Mathcad 2001, I have an exercise on differientiation cannot make work

2. Post exactly what you are trying to do.
Post a screen-shot if possible.

3. ## Differentiation

[IMG]file:///C:/DOCUME%7E1/OPENUN%7E1/LOCALS%7E1/Temp/moz-screenshot.jpg[/IMG][IMG]file:///C:/DOCUME%7E1/OPENUN%7E1/LOCALS%7E1/Temp/moz-screenshot-1.jpg[/IMG][IMG]file:///C:/DOCUME%7E1/OPENUN%7E1/LOCALS%7E1/Temp/moz-screenshot-2.jpg[/IMG][IMG]file:///C:/DOCUME%7E1/OPENUN%7E1/LOCALS%7E1/Temp/moz-screenshot-3.jpg[/IMG][IMG]file:///C:/DOCUME%7E1/OPENUN%7E1/LOCALS%7E1/Temp/moz-screenshot-4.jpg[/IMG] I have to use the symbolic differentiation and the 'simplify' keyword to find an expression for the derivative of f'(x). (you may need to put x=x in your worksheet)
Now my function is

f(x)= 8x(5-2x)(13+2x)/(2+x)^2

When I simplify it give

8x(5-2x) (13+2x)/(2+x)^2

It doesn't look right for a derivative of f'(x), it just change to (13+2x)/(2+x)^2.

Hope you understand. I try screenshot and attached my file, it's not working

[IMG]file:///C:/DOCUME%7E1/OPENUN%7E1/LOCALS%7E1/Temp/moz-screenshot-7.jpg[/IMG]

4. This is what MathCad gives me.

Oh, I try the dx function but it is not working for me. Next exercise ask to solve the equation f'(x)=0 (using a solve block), I try with your result and give me a massive page of calculation, but they ask the answer to 6 d.p.

Don't know what I'm doing wrong

6. Originally Posted by valerie-petit
f'(x), it just change to (13+2x)/(2+x)^2
That certainly makes no sense. My first suspicion is an input error.

How careful are you to use EXPLICIT multiplication when you enter your expressions?

Are you SURE you don't have part of your expression entered as text?

7. Here is the next question.

[IMG]file:///C:/DOCUME%7E1/OPENUN%7E1/LOCALS%7E1/Temp/moz-screenshot-11.jpg[/IMG][IMG]file:///C:/DOCUME%7E1/OPENUN%7E1/LOCALS%7E1/Temp/moz-screenshot-12.jpg[/IMG]

I attached my files, the first line I try under f(x), the Third line is the way you did it with dx and the middle one is when I try to solve it.

Hope the attachment works

9. Two points.
Why do you have $x:=x$?
Try using $(8 \cdot x)$ instead of $8x$.

It works for simplify, you were right I put 8x under brackets and it works

Sorry Plato with all my questions, but in the second question to solve the equation f'(x)=0, it said that my answer should be in 6 decimal places, but like you it gave me different calculations not one result.

12. Once you ask it to "solve for" and the blue backwards L is on the solution then type = key to change to decimal format. Once in decimal form, double click on a real number and you then can format the number of places you need.

Ok, sorry I saw the calcution but didn't scroll to the end of my screen, I change in format to 6 d.p and it gave 0.8531; -3.42655+5.133725i etc...

Did you find the same results

14. Originally Posted by valerie-petit
Ok, sorry I saw the calcution but didn't scroll to the end of my screen, I change in format to 6 d.p and it gave 0.8531; -3.42655+5.133725i etc...

Did you find the same results
Set not only the number of decimals but also the “exponential threshold”.
The other two numbers are complex numbers. I think you want the real solutions.