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<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>
<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>
<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>

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Differentiation

The function y(x) is given by y(x) = x^3 - 3x.

Calculate the intervals on which y is (a) increasing, (b) decreasing.

Thanks!:smile:
Reply 1
Avatar for Retropmot
Retropmot
a) its increasing when dy/dx>0
dy/dx = 3x^2 - 3
so find when 3x^2 - 3>0
3x^2>3
x^2>1
so x>1 or x<-1

b)decreasing when dy/dx<0
so find when 3x^2<3
x^2<1
-1<x<1
Reply 2
Avatar for devesh254
devesh254
OP
The answers I have got here are:

(a) (-inf, -1) and (1, inf)
(b) (-1,1)

So (b) is fine...anyone know how to get (a)? Or is the textbook wrong?

Thanks again :smile:
Reply 3
Avatar for kikzen
kikzen
14
devesh254
The answers I have got here are:

(a) (-inf, -1) and (1, inf)
(b) (-1,1)

So (b) is fine...anyone know how to get (a)? Or is the textbook wrong?

Thanks again :smile:

those are the answers hes got...
Reply 4
Avatar for devesh254
devesh254
OP
ah yeh...thx

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