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C3 Trig - Tricky?! Watch

integral of sinx^2 cosx

Thanks
2. what is ?
3. (Original post by TimmonaPortella)
what is ?
cosx
4. (Original post by asem93)
cosx
so, what substitution do you think you should make?
5. (Original post by TimmonaPortella)
so, what substitution do you think you should make?
u = sin x
du/dx = cos x
6. (Original post by asem93)
u = sin x
du/dx = cos x
7. (Original post by TimmonaPortella)
lol, I know that

but what after...
8. To clarify, is that or ?
Then I'll take you through the first steps and see if you can go from there.
9. (Original post by TimmonaPortella)
To clarify, is that or ?
Then I'll take you through the first steps and see if you can go from there.
I'm sure you know that the former option would not be Core 3.
10. (Original post by TimmonaPortella)
To clarify, is that or ?
Then I'll take you through the first steps and see if you can go from there.
it is
11. (Original post by asem93)
it is
In future, call it as this notation avoids any confusion.
12. (Original post by Mr M)
In future, call it as this notation avoids any confusion.
Yes, sorry.
13. (Original post by asem93)
Yes, sorry.
You don't need to be sorry! Anyway, what does the substitution u = sin x transform your integral into?

Edit: I'm wondering if the fact that you have forgotten to include dx at the end of your integral is causing you a problem.
14. (Original post by Mr M)
You don't need to be sorry! Anyway, what does the substitution u = sin x transform your integral into?
What do you mean transform? is that the integral of u^2 cosx
15. (Original post by Mr M)
You don't need to be sorry! Anyway, what does the substitution u = sin x transform your integral into?

Edit: I'm wondering if the fact that you have forgotten to include dx at the end of your integral is causing you a problem.
Ah I see.. I did forget it's dx... but what is the significance of that anyway?
16. (Original post by asem93)
What do you mean transform? is that the integral of u^2 cosx
Ok that is definitely your problem.

17. (Original post by asem93)
Ah I see.. I did forget it's dx... but what is the significance of that anyway?
Have you been taught integration by substitution yet?
18. (Original post by Mr M)
Ok that is definitely your problem.

Okay so the integral of u^2 is u^3/3 but what is the int of du??
19. (Original post by asem93)
Okay so the integral of u^2 is u^3/3 but what is the int of du??
I don't want to answer that question as it will reinforce your misconception.

The integral of u^2 is meaningless.

The integral of u^2 du is u^3/3.

The du bit isn't just there to look pretty, it is as vital as putting your trousers on when you go to the shops.
20. Double Angle Formula to define sin^2x in terms if cos2x..

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