# inverse functions

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in the Dr F maths ppt it says that 'if the function is equal to its inverse, it must lie on the line y=x. f(x)=x. '

not tryna sound stupid but y=1/x is equal to its inverse but f(x) isn't equal to x?

not tryna sound stupid but y=1/x is equal to its inverse but f(x) isn't equal to x?

Last edited by Htx_x346; 1 month ago

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#2

(Original post by

in the Dr F maths ppt it says that 'if the function is equal to its inverse, it must lie on the line y=x. f(x)=x. '

not tryna sound stupid but y=1/x is equal to its inverse but f(x) isn't equal to x?

**Htx_x346**)in the Dr F maths ppt it says that 'if the function is equal to its inverse, it must lie on the line y=x. f(x)=x. '

not tryna sound stupid but y=1/x is equal to its inverse but f(x) isn't equal to x?

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(Original post by

Can you upload a pic of the slide?

**mqb2766**)Can you upload a pic of the slide?

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#4

(Original post by

er not really...i can put a link to the slides though and tell you the slide no.?

**Htx_x346**)er not really...i can put a link to the slides though and tell you the slide no.?

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sure

**mqb2766**)sure

https://www.drfrostmaths.com/resource.php?rid=303

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#6

**Htx_x346**)

in the Dr F maths ppt it says that 'if the function is equal to its inverse, it must lie on the line y=x. f(x)=x. '

not tryna sound stupid but y=1/x is equal to its inverse but f(x) isn't equal to x?

Last edited by RichE; 1 month ago

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(Original post by

sure

**mqb2766**)sure

Last edited by Htx_x346; 1 month ago

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(Original post by

I can't see the slides but this clearly isn't true. It needs to have reflective symmetry in the line y=x. For example f(x)=1-x is another such self-inverse function.

**RichE**)I can't see the slides but this clearly isn't true. It needs to have reflective symmetry in the line y=x. For example f(x)=1-x is another such self-inverse function.

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#9

**Htx_x346**)

in the Dr F maths ppt it says that 'if the function is equal to its inverse, it must lie on the line y=x. f(x)=x. '

not tryna sound stupid but y=1/x is equal to its inverse but f(x) isn't equal to x?

He says y-x is line of symmetry for f and its inverse.

Last edited by mqb2766; 1 month ago

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(Original post by

From what I can see on the slide 26 (and the usual explanation) is f and f^(-1) are reflections in y-x line. The reciprocal you mention is a self inverse (involution) so its equal to its own reflection.

He says y-x is line of symmetry for f and its inverse.

**mqb2766**)From what I can see on the slide 26 (and the usual explanation) is f and f^(-1) are reflections in y-x line. The reciprocal you mention is a self inverse (involution) so its equal to its own reflection.

He says y-x is line of symmetry for f and its inverse.

thanks

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#11

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oh i'm just being stupid..it meant you can equate f(x)=x when you're trying to find the intersection of f(x)=f^-1(x).

thanks

**Htx_x346**)oh i'm just being stupid..it meant you can equate f(x)=x when you're trying to find the intersection of f(x)=f^-1(x).

thanks

The reflection of 1/x is 1/x hence the self inverse property or f(f(x)) = x

Last edited by mqb2766; 1 month ago

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(Original post by

It just means f^(-1) s a reflection of f in the line y=x and vice versa.

The reflection of 1/x is 1/x hence the self inverse property or f(f(x)) = x

**mqb2766**)It just means f^(-1) s a reflection of f in the line y=x and vice versa.

The reflection of 1/x is 1/x hence the self inverse property or f(f(x)) = x

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#13

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hmmm

**Htx_x346**)hmmm

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#14

**Htx_x346**)

oh i'm just being stupid..it meant you can equate f(x)=x when you're trying to find the intersection of f(x)=f^-1(x).

thanks

And in this case f(x)=x is a lot easier to solve than f(x)=f^(-1)(x)

Last edited by RichE; 1 month ago

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(Original post by

Think about the graphs of ln() and exp() or ... they're reflections in y=x.

**mqb2766**)Think about the graphs of ln() and exp() or ... they're reflections in y=x.

Last edited by Htx_x346; 1 month ago

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(Original post by

I imagine this is what's meant here for this specific function (which isn't self-inverse).

**RichE**)I imagine this is what's meant here for this specific function (which isn't self-inverse).

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(Original post by

Can you expand somewhat?

**RichE**)Can you expand somewhat?

(Original post by

I imagine this is what's meant here for this specific function (which isn't self-inverse).

And

**RichE**)I imagine this is what's meant here for this specific function (which isn't self-inverse).

And

**in this case f(x)=x is a lot easier to solve than f(x)=f^(-1)(x)**
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