Using 4U knowledge in 3U exam? (1 Viewer)

[the_king]

Can i use 4U techniques in the HSC for 3U or any other 3U exam??

For Example: find area of a curve y=ln(x-1) from 2 to e+1. Its worth 4 mark and require integrating ln(x-1), so could i just use integration by parts and get the answer or do i have to do the 3U way of find in terms of y?

 

[strawberrye]

I think you can, use whatever technique is the easiest/most appropriate for the question. As long as you get the right answer with a methodical approach, that's all it matters(however do check with your teacher whether they would allow this)

 

[Kurosaki]

You shouldn't need to use 4U techniques, and at my school it's frowned upon. I guess you could do it if you derived integration by parts.

 

[Carrotsticks]

The 3U HSC is designed such that 4U knowledge will give you minimal advantage.

Also, using integration by parts will take a bit longer to do than the '3U method'

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[Verify]

You can but you wouldn't

 

[QZP]

The 3U HSC is designed such that 4U knowledge will give you minimal advantage.

Also, using integration by parts will take a bit longer to do than the '3U method'

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Is the 3U method considering d/dx (x-1)ln(x-1) - x ? (Obtained from playing around with d/dx (x-1)ln(x-1) to eventually get it)

 

[rumbleroar]

strongly recommended you don't
use 3u methods in a 3u test because that's what they're testing you on

 

[Kurosaki]

Is the 3U method considering d/dx (x-1)ln(x-1) - x ? (Obtained from playing around with d/dx (x-1)ln(x-1) to eventually get it)

I think from what they said in their post, OP means considering the rectangle formed by the axes, y=1 and x=e+1, and then finding x in terms of y, then integrating to find the area bounded by y=1, the y axis and the given curve, and subtracting that area.
I.e. the rectangle formed has an area of e+1 units.


If we compute the integral , we can find the area between the curve and the y-axis. We can that subtract that area from the area of the rectangle to find the area between the curve and the x-axis.

Edit: Btw your method is pretty much IBP in disguise lol

 

[cutemouse]

Can i use 4U techniques in the HSC for 3U or any other 3U exam??

For Example: find area of a curve y=ln(x-1) from 2 to e+1. Its worth 4 mark and require integrating ln(x-1), so could i just use integration by parts and get the answer or do i have to do the 3U way of find in terms of y?

Yes, but note what was said in the marker's comments for Q2(c)(ii) of the 2005 Extension 1 HSC paper:

"Some candidates tried to use integration by parts to do this question. However, very few were successful using this method."