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September 28, 2025, 04:01:51 am

Author Topic: do I have to be able to do this by hand?  (Read 1661 times)  Share 

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wombifat

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do I have to be able to do this by hand?
« on: April 07, 2009, 10:11:55 pm »
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for questions asking for the point of intersections between the function and its inverse

eg. 2loge(x=3)+4 find the inverse function and the coordinates of the points of intersection of the graphs f(x)=y and y=f^-1(x)

can we just do that using the calculator? Or do we need to know how to do this by hand?

Flaming_Arrow

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Re: do I have to be able to do this by hand?
« Reply #1 on: April 07, 2009, 10:13:03 pm »
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you can do it on the calc
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wombifat

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Re: do I have to be able to do this by hand?
« Reply #2 on: April 07, 2009, 10:14:27 pm »
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so it won't come up on the tech free exam?

TrueTears

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Re: do I have to be able to do this by hand?
« Reply #3 on: April 08, 2009, 12:57:44 am »
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If the inverse intersects with original. You can always do the simultaneous equation with y = x. (As the inverse and original will intersection on the line y = x)

There will be a high probability a question like this might appear in the tech free.
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Mao

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Re: do I have to be able to do this by hand?
« Reply #4 on: April 08, 2009, 08:50:37 am »
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If the inverse intersects with original. You can always do the simultaneous equation with y = x. (As the inverse and original will intersection on the line y = x)

There will be a high probability a question like this might appear in the tech free.

that is partially correct. For this method to work, the graph must not be symmetrical about

consider the graph , or a quarter circle . There are infinite number of solutions to

Hence, graphing is very important. Though for the sake of tech-free exam one, the method TT described would be sufficient [as they are not going to give you a psycho function that requires a calculator to solve for intersections not on y=x]
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NE2000

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Re: do I have to be able to do this by hand?
« Reply #5 on: April 08, 2009, 01:01:49 pm »
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If the inverse intersects with original. You can always do the simultaneous equation with y = x. (As the inverse and original will intersection on the line y = x)

There will be a high probability a question like this might appear in the tech free.

Yeah but is there any way you could do that on tech free with wombifat's y = 2loge(x-3) + 4??
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wombifat

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Re: do I have to be able to do this by hand?
« Reply #6 on: April 08, 2009, 03:39:35 pm »
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so would you find the original graph's intersection with y=x?

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Re: do I have to be able to do this by hand?
« Reply #7 on: April 08, 2009, 03:43:14 pm »
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You can use either the original or the inverse.

And, just like Mao said, do a quick sketch of the graph to get an idea of what it looks like.
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wombifat

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Re: do I have to be able to do this by hand?
« Reply #8 on: April 08, 2009, 03:45:27 pm »
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yeah sketching a graph was part of the question anyway :P
thanks a lot, I never got told how to do questions like that without a calculator