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Algebra

Scorching goIITian

 Joined: 31 Oct 2007 Post: 227
1 Feb 2008 12:31:42 IST
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6
450
another on functions
Engineering Entrance , JEE Main , JEE Main & Advanced , Mathematics , Algebra

f(x)=(2x- )^3 +2x-cosx. the value of d/dx f inverse of x,x=

#### Comments (6)

Blazing goIITian

Joined: 31 Jan 2008
Posts: 334
1 Feb 2008 12:42:44 IST
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is the ans. 1/2
if yes then i will give the sol...

Scorching goIITian

Joined: 31 Oct 2007
Posts: 227
1 Feb 2008 13:12:59 IST
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the ans is 1/3. & i got it too

Blazing goIITian

Joined: 9 Jan 2008
Posts: 843
1 Feb 2008 13:14:44 IST
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could u post the solution

Blazing goIITian

Joined: 31 Jan 2008
Posts: 334
1 Feb 2008 16:00:32 IST
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look i am sending u a trick
plz. rate me for it......
when u want to get some inverse, then just exchange the places of x and y. u can know it if u apply pure logic. remember: (f inv.) is reflection of f on line y=x
like here-
x=(2y-pie)3 +2y- cosy  ...............  A      y =f(x)
this is the inv. of given fn.
now see for x=pie we get y=pie/2 as one ans.
so differentiate A....
and put y=pie/2   as x=pie
putting values we can get ans.
if any prob. nudge me!! or else...

PLZ. RATE ME IF U LIKE IT. i request it to all of u....

Blazing goIITian

Joined: 31 Jan 2008
Posts: 334
1 Feb 2008 17:12:35 IST
0 people liked this

hey the ans is 1/2
and i am sure

Blazing goIITian

Joined: 25 Aug 2007
Posts: 521
1 Feb 2008 17:35:06 IST
1 people liked this

This can be taken as a result d[ f-1(x)]/dx = reciprocal of d[f(x)] / dx

Here d[f(x)]/dx at x=pi/2 is 3.

So d[ f-1(x)]/dx = 1/3.

@saurabh : I think u'll get 1/3 with ur method also. just check ur working

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