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A-Level Differentiation Part 2

Stuck again.

Question:
The maximum point on the curve with the equation y=xsin^0.5x where 0<x<pi is A. Show that the x coordinate of A satisfies the equation 2tanx+x=0.


I've differentiated it to sin^0.5x +xcosx/2sin^0.5x, but cant work out how to get the maximum point.
set the differential equal to zero, take out sinx as a common factor
Original post by LukeMontgomery
Stuck again.

Question:
The maximum point on the curve with the equation y=xsin^0.5x where 0<x<pi is A. Show that the x coordinate of A satisfies the equation 2tanx+x=0.


I've differentiated it to sin^0.5x +xcosx/2sin^0.5x, but cant work out how to get the maximum point.


set **sin^0.5x +xcosx/2sin^0.5x to zero

multiply each term by *sin^0.5x

to get tanx you need to think of sinx/cosx ....*
Original post by the bear
set **sin^0.5x +xcosx/2sin^0.5x to zero

multiply each term by *sin^0.5x

to get tanx you need to think of sinx/cosx ....*


If I times both sides by sin^0.5x then I get sinx+xcosx/2=0

What do I do from there?
Original post by LukeMontgomery
If I times both sides by sin^0.5x then I get sinx+xcosx/2=0

What do I do from there?


you need to somehow get tanx to appear.... *
Original post by the bear
you need to somehow get tanx to appear.... *


sinx+xcosx/2=0

2sinx+xcosx=0

2sinx/cosx+xcosx/cosx=0

=2tanx+x=0

Ok so I've done that, but how do I work out the x coordinate of A.
Original post by LukeMontgomery
sinx+xcosx/2=0

2sinx+xcosx=0

2sinx/cosx+xcosx/cosx=0

=2tanx+x=0

Ok so I've done that, but how do I work out the x coordinate of A.


You don't have to. It simply asks you to show that it satisfies that equation and you've done it. It's a transcendental equation anyhow so you cannot solve it using analytical methods, unless you say x=0 but that's not the only solution.
(edited 7 years ago)
Original post by RDKGames
You don't have to. It simply asks you to show that it satisfies that equation and you've done it. It's a transcendental equation anyhow so you cannot solve it using analytical methods, unless you say x=0 but that's not the only solution.


Ok good, thanks!
you could use something like the Newton-Raphson method to solve it after that.

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