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Product rule - Differentiation

Nkhan

Use the product rule to differentiate xtanx

The answer in the book says tanx+xsex^2x

Does it matter if you write xsec^2x + tanx though?

Reply 1

wizz_kid

Original post by Nkhan

Use the product rule to differentiate xtanx

The answer in the book says tanx+xsex^2x

Does it matter if you write xsec^2x + tanx though?

Mate ur doing a-level and i cant believe that you dont seem to know that it is the same thing. They are commutative :

A+B = B+A

Reply 2

nufc_joe

hahahahahahhahaha but no it doesnt matter

Reply 3

Noble.

No. According to the commutative law a+b=b+a, so both those expressions are identical. All you've done is swapped u and v in this:

\frac{d}{dx}(uv) = \frac{du}{dx}v + u\frac{dv}{dx}

Reply 4

Nkhan

Original post by wizz_kid

Mate ur doing a-level and i cant believe that you dont seem to know that it is the same thing. They are commutative :

A+B = B+A

Lool ayy low me :|

Reply 5

dnumberwang

Original post by Nkhan

Use the product rule to differentiate xtanx

The answer in the book says tanx+xsex^2x

Does it matter if you write xsec^2x + tanx though?

I'm wondering why the book has made a 'sex' function

Reply 6

APonderingMind

Easy

Edit:... yeh so I kind of jumped to conclusion, thinking you didn't know how to solve it, and didn't read your thread properly. The order doesn't matter since they are both positive values.... you really should know by this stage of maths already....

(edited 13 years ago)

Reply 7

Nkhan

Original post by dnumberwang

I'm wondering why the book has made a 'sex' function

Lool sorry about that, my typo error I guess :/

Reply 8

Chelle-belle

Original post by APonderingMind

Easy

Are you sure that is the reason why.

Original post by Nkhan

Lool sorry about that, my typo error I guess :/

Don't worry about people like that. But it's nevertheless important that you know how to check and have confidence in your own answers.
Easy way to check if your answer is the same is by putting in numbers. Essentially xsec^2x + tanx are going to be just numbers. Does 5+6=6+5? Yep. So you have every right to be confident that you can write (xsec^2x + tanx) or (tanx + xsec^2x) as your answer, because they are the same. As long as you get the right answer and you do what they ask you to do, they will allow different forms of the same answer like you have given.

(edited 13 years ago)

Reply 9

IrrationalNumber

Original post by APonderingMind

The order doesn't matter since they are both positive values

You can say something stronger than that...

Reply 10

boromir9111

Original post by dnumberwang

I'm wondering why the book has made a 'sex' function

Darn....you beat me to it :tongue:

Reply 11

APonderingMind

Original post by Chelle-belle

Are you sure that is the reason why.

...why exactly are we having a debate over something as simple as this? It's actually insulting my intelligence. =/

You tell me then, is 4+2 the same as 2+4? Is 2-4, the same as 4-2?

Jeez, what a way to waste time.

Reply 12

APonderingMind

Original post by IrrationalNumber

You can say something stronger than that...

I could, but if the OP doesn't even understand the basic rules of maths, should I dwell into it any further?

If it makes you happy:

A + B = B + A

A - B = -B + A

B - A = -A + B

Reply 13

?!master?!mini?!

Original post by APonderingMind

trick question????????

yes and no

Reply 14

IrrationalNumber

Original post by APonderingMind

I could, but if the OP doesn't even understand the basic rules of maths, should I dwell into it any further?

If it makes you happy:

A + B = B + A

A - B = -B + A

B - A = -A + B

It's the fact that you mention them being positive values that bothers me. The fact that they are positive has no bearing on them being commutative under addition or not. In fact, tan isn't everywhere positive and neither is xsec^2x.

Reply 15

Chelle-belle

Original post by APonderingMind

It's actually insulting my intelligence. =/

Sorry, I didn't mean to insult your intelligence. My issue is the same as the one above, and my post was to make you think about what was off about your reason. And it's not (or was not) really a debate (yet).