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• September 13th 2008, 04:03 AM
valerie-petit
Hi everyone,

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

(Itwasntme)
• September 13th 2008, 04:27 AM
Plato
Post exactly what you are trying to do.
Post a screen-shot if possible.
• September 13th 2008, 05:40 AM
valerie-petit
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(Headbang)

[IMG]file:///C:/DOCUME%7E1/OPENUN%7E1/LOCALS%7E1/Temp/moz-screenshot-7.jpg[/IMG]
• September 13th 2008, 05:52 AM
Plato
This is what MathCad gives me.
• September 13th 2008, 06:27 AM
valerie-petit
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
• September 13th 2008, 06:31 AM
TKHunny
Quote:

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?
• September 13th 2008, 06:40 AM
Plato
Here is the next question.
• September 13th 2008, 07:13 AM
valerie-petit
[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
• September 13th 2008, 07:23 AM
Plato
Two points.
Why do you have $x:=x$?
Try using $(8 \cdot x)$ instead of $8x$.
• September 13th 2008, 07:32 AM
valerie-petit
It works for simplify(Clapping)(Clapping)(Clapping), you were right I put 8x under brackets and it works(Giggle)(Rofl)
• September 13th 2008, 07:35 AM
valerie-petit
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.
• September 13th 2008, 07:52 AM
Plato
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.
• September 13th 2008, 08:03 AM
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(Worried)
• September 13th 2008, 08:20 AM
Plato
Quote:

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(Worried)

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.
• September 13th 2008, 08:28 AM
valerie-petit