Makro
Porcupine
Silly that you can't use latex for the starting of a topic, so I'll reply with the question 
Indefinite integral (1 Viewer)
- Thread starter Makro
- Start date
Makro
Porcupine
My Solution
Solution:
Last edited:
lychnobity
Active Member
- Joined
- Mar 9, 2008
- Messages
- 1,292
- Gender
- Undisclosed
- HSC
- 2009
Since you have the derivative of -x^3 (ie 3x^2) you don't need to integrate that. Just integrate the brackets.
Timothy.Siu
Prophet 9
do u know the chain rule?
if u differentiate ur answer, u can clearly see it is incorrect.
if u differentiate ur answer, u can clearly see it is incorrect.
Makro
Porcupine
I don't think I remember it, glanced at it in my textbook and it looked weird, care to explain it for me?
Timothy.Siu
Prophet 9
so do u know how to differentiate (x2-1)4 for example?
it becomes,4(x2-1)3 . 2x which means that u have to multiply d/dx (x2-1) to the result which is basically the idea of the chain rule. and d/dx (x2-1)=2x
also, ur idea of integration is wrong, if u want to integrate two things multiplied together, u dont just integrate both of them...like what u did above.
also this question would most likely be a 3unit question although it could possibly be in the 2unit paper but i'm pretty sure they'd give u some help or a lead in
Last edited:
Makro
Porcupine
Right, right. Yeah I knew that chain rule. So the chain rule is the same for integration? Just the work we've gotten hadn't really shown us that.
Just to see if I get this correctly, you divide by -3x^2 because you integrate the value in the brackets and then divide by 5 and add 1 to the power. This cancels out with the 3x^2 on the numerator and so you're left with a negative fraction and then that's the correct solution? Or did my logic fail again? heh.
Just to see if I get this correctly, you divide by -3x^2 because you integrate the value in the brackets and then divide by 5 and add 1 to the power. This cancels out with the 3x^2 on the numerator and so you're left with a negative fraction and then that's the correct solution? Or did my logic fail again? heh.
Timothy.Siu
Prophet 9
yeah u basically got it, but i'm not if thats mathematically correct
basically, since u know that -3x2 is the derivative of the bracketed thing, u dont have to worry about it when u integrate it, u just have to worry about the bracketed bit since u know that when u differentiate it, you'll have the 3x2, hmm its sorta complicated explaining it for 2unit maths.
Makro
Porcupine
Oh wait I typed the wrong thing. You differentiate inside the brackets but integrate outside. then you'll get the 3x^2 to cancel out leaving only a negative or a -1 and then that gets to the solution. It seems like if I do that I'd get these sorts right. It was on a different worksheet which was just for extra revision so I doubt it'll be in my half yearly.
Thank you heaps
Thank you heaps
Timothy.Siu
Prophet 9
your welcome.Oh wait I typed the wrong thing. You differentiate inside the brackets but integrate outside. then you'll get the 3x^2 to cancel out leaving only a negative or a -1 and then that gets to the solution. It seems like if I do that I'd get these sorts right. It was on a different worksheet which was just for extra revision so I doubt it'll be in my half yearly.
Thank you heaps
yeah i guess thats right, if it works then its right. and yeah i doubt they'll ask it, its not really a 2unit question