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Let y=sin(n*sin^-1x), n>0.Show that: (1 - x^2)*y" - xy' + n^2y=0

 Feb 14, 2016
 #1
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Is this Chebyshev's equation: (1 - x^2)*y" - xy' + n^2y=0   ???????

 Feb 14, 2016
 #2
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y = sin (n * arcsin x)   n > 0

 

y '  =  cos (n*arcsin x) * [ n  (1 - x^2)^(-1/2)]

 

y ''  = -sin(n*arcsin x) * [ n  (1 - x^2)^(-1/2)]* [ n  (1 - x^2)^(-1/2)]  + cos(n * arcsinx)* [n * x * (1 - x^2)^(-3/2) ] =

 

-sin(n*arcsin x)* [n^2 (1- x^2)^-1] + cos (n*arcsinx) * [ nx * (1- x^2)^(-3/2) ]  =

 

[n (1-x)^(-3/2)] * [ xcos(n*arcsinx  - nsin(n*arcsinx)(1-x^2)^(1/2) ]

 

So....

 

(1 - x^2) y ''  - xy '  + n^2y    =

 

(1-x^2) [n (1-x)^(-3/2)] [ xcos(n*arcsinx)- nsin(n*arcsinx)(1-x^2)^(1/2)] -

x [cos (n*arcsin x)] * [ n  (1 - x^2)^(-1/2)]  + n^2 [sin (n * arcsin x)]  =

 

 

[ n (1 -x)^(-1/2) ] [ xcos(n*arcsinx)  - nsin(n*arcsinx)(1-x^2)^(1/2) ] 

- x [cos (n*arcsin x)] * [ n  (1 - x^2)^(-1/2)]  + n^2 [sin (n * arcsin x)]   =

 

 

[ xcos(n*arcsinx)] *  [ n (1 -x)^(-1/2) ] -

[ n (1 -x)^(-1/2) ] * [ nsin(n*arcsinx)(1-x^2)^(1/2)] -

[x cos (n*arcsin x)] * [ n  (1 - x^2)^(-1/2)]  + n^2 [sin (n * arcsin x)]   =

 

n^2 [sin (n * arcsin x)]  -

 n * (1 -x)^(-1/2)  * [ nsin(n*arcsinx)] * (1-x^2)^(1/2)  =

 

n^2 [sin (n * arcsin x)]   -  [ n* n * (1 -x)^(-1/2) * (1 -x)^(1/2) * sin(n*arcsinx) ] =

 

n^2 [sin (n * arcsin x)]  - n^2 [ sin(n * arcsinx)]  =

 

0

 

 

 

cool cool cool

 Feb 14, 2016
edited by CPhill  Feb 14, 2016
edited by CPhill  Feb 14, 2016
edited by CPhill  Feb 14, 2016
edited by CPhill  Feb 14, 2016
edited by CPhill  Feb 14, 2016
edited by CPhill  Feb 14, 2016
edited by CPhill  Feb 14, 2016
edited by CPhill  Feb 14, 2016

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