Question

f(x)=2sinxcosx, what is the primitive function?

Answer 1

you have to find f'(x)

Answer 2

That would be f'(x)=2cos^2(x)-2sin^2(x)

Answer 3

I believe atleast, having such a hard time following productrules et cetera backwards.. :x

Answer 4

\[\Large f'(x)=(2 \cdot \sin x \cdot \cos x)'\]

take number 2 off...

\[\Large f'(x)=2( \sin x \cdot \cos x)'\] and go on...

Answer 5

http://www.sosmath.com/CBB/viewtopic.php?f=3&t=57694 the same problem I had before !

Answer 6

I think you're supposed to rewrite the function into something more manageable.

Answer 7

Perhaps by trigonometric identities or w/e, bah - clueless here!

Answer 8

I don't understand you O_O

Answer 9

is in the link what you're asking for or not ? ...(Google translate sucks !)

Answer 10

Sorry, English is not my native language and I take math in Sweden - quite hard to "translate" the math into English, hehe.

Answer 11

I cant put the thing you linked into context, hmm

Answer 12

Primitive means antiderivative so integrate it.
\[\int\limits2sinxcosx \]
let u = cosx => du/-sinx

Answer 13

@Mimi_x3 but how? ... then my task there was wrong , wan't it ? O_O

Answer 14

I'm aware of that Mimi_x3
The thing is - I don't know how to do it! :D

Answer 15

I remember when primitive means to integrate..

Answer 16

not differentiate.

Answer 17

Indeed it is the antiderivative.

Answer 18

aufff... then I apologize , I learned it wrong :( ... thanks for explaining it @Mimi_x3

Answer 19

Well, it's a u-substitution.

Answer 20

Hm, but I'm not sure, lol.

Answer 21

You're supposed to do it without substitution I believe, as the book I have explains substitution in the upcoming chapter.

Answer 22

You can work backwards..when you find the derivative i think..

Answer 23

I think what you basicly should do is use the product rule backwards, or rewrite it with the help of some trig identity.

Answer 24

Indeed, it's very tiresome and confusing though, haha :(

Answer 25

.. if it's integral ... then check this out ! ... http://www.wolframalpha.com/input/?i=2sinxcosx

Answer 26

But she has not learnt u-substition.

Answer 27

PRIMITIVE = INTEGRAAAAAALLLL!!!!!

Answer 28

I'm out !

Answer 29

write that as sin2x. then integrate using std. formula!!! should get
----> (-cos2x)/2 + constant

Answer 30

I shall try, thanks everyone!