functions

prove that the solution(s) of f(x) = inverse of f(x) lie either on the line y = x or on a line whose slope is -1.

17 Answers

1
pritishmasti ............... ·

as the inverse of a curve is it's image about y=x line so if the two curves intersect they will do so on y = x line for sure there would be no case when inverse and original curve intersect and they don't do it on y=x line
The second case is just an additional one ie if the two curves intersect on a line with slope=-1 they will do it in addition to intersecting on y=x line

eg f(x) = x2 , f-1(x) = x1/2

they intersect on (0,0) and (1,1)
case I(y=x)
both points are on y=x
case II(slope = -1)
(0,0) is on y=-x (slope =-1)
(1,1) is on y=2-x (slope =-1)

the image is a bit out of scale

both the cases are simutaneously applicable for the curves which intersect with it's inverse

6
AKHIL ·

so guys what shud be the final answr??

6
AKHIL ·

well the quesn is like this only!!!:P

341
Hari Shankar ·

The wording of the question is itself so imprecise.

every point lies on a line with slope =-1!

1
ujjwalkalra kalra ·

i meant same..akhil try to get our point

1
pritishmasti ............... ·

akhil you didn't read my lines properly...i said that if they do intersect then they will do it on y=x line ...if they don't(as in your figure) then surely they can't intersect on y=x
can you give me any example where a curve and it's inverse are intersecting and they are not doing it on y=x line

39
Pritish Chakraborty ·

Self-invertible functions like f(x) = 1/x, x ≠0 will not follow this property. It is often wrongly assumed that the number of solutions of the function and its inverse are the number of solutions of the function and line y = x. This is incorrect because self-invertibles possess infinite solutions apart from y = x.
By self-inverse, I mean some functions are their own inverses.

1
ujjwalkalra kalra ·

then the inverse dnt exsit take example of{x}

6
AKHIL ·

well it is not so........
in some cases the curve and its image wont intersect at y = x.....

see

6
AKHIL ·

sum 1 plzzz try!!!!

1
ujjwalkalra kalra ·

is it so...r u sure about ur second statement...dude thn plz gve me example...

6
AKHIL ·

well what abt the second case then??
its not necessary that all the functions and their inverses intersect at y = x...

1
ujjwalkalra kalra ·


now carefully observe the equation f(x)=f-1(x) .....u will see tht they will only intersect at y=x..

i hope nw ur doubt is clear

6
Kalyan IIT-K Beware I'm coming ·

inverse f(x) means mirror image of graph along y=x line.
slope = -1 means that y=-x
.
correct me if am wrong!!!
thinking what else to do...

6
AKHIL ·

well i m having prob with the 2nd part of the quesn!!!!

1
prateek mehta ·

the answer is only y=x ...such that the slope is always 1
..

i cannot prove but try examples ...and then check for conditions arising..

341
Hari Shankar ·

f(x) = 1/x, x≠0 seems to be a counterexample. Any missing conditions?

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