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# integration (reverse chain rule) watch

1. how do i integrate sin4x using the reverse chain rule the book doesn't explain it well
2. (Original post by man111111)
how do i integrate sin4x using the reverse chain rule the book doesn't explain it well
Same as any other function where the inside is linear. Just integrate the function as normal then divide by the derivative of the linear.
3. You can use substitution, by letting u=4x and so on.
However, for the reverse chain rule, it's easy to integrate sin(4x) to get -cos(4x), then divide by the derivitative of the bracket.
For sin(4x), the derivative of the bracket is 4.
Therefore, you get -1/4cos(4x) + c
4. (Original post by geedot)
You can use substitution, by letting u=4x and so on.
However, for the reverse chain rule, it's easy to integrate sin(4x) to get -cos(4x), then divide by the derivitative of the bracket.
For sin(4x), the derivative of the bracket is 4.
Therefore, you get -1/4cos(4x) + c
i would use that way but the book asks for the reverse chain rule. do you think i can use any method to integrate during an exam(AQA)? i dont think ive seen a past paper where it says use the reverse chain rule
5. (Original post by man111111)
i would use that way but the book asks for the reverse chain rule. do you think i can use any method to integrate during an exam(AQA)? i dont think ive seen a past paper where it says use the reverse chain rule
Yeah I'm pretty sure. After all, the teaching method for the reverse chain rule usually varies from school to school anyway. They're usually more strict about method with substitution and things
6. (Original post by man111111)
i would use that way but the book asks for the reverse chain rule. do you think i can use any method to integrate during an exam(AQA)? i dont think ive seen a past paper where it says use the reverse chain rule
Reverse chain rule is just a result that comes from substitution. You can use substitution or "reverse chain rule" in an exam.

Most students know that the integral of e.g. sin(4x) is -1/4 cos(4x) + c without having to go through the motions of substitution.

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Updated: March 1, 2018
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