The Student Room Group

Tricky differentiation question

Given that y=e^-x.cosx, show that d^2y/dx^2+2(dy/dx)+2y=0

Absolute pain in the backside...I got as far differentiating and then differentiating again so I'm left with the mess of tidying it up :redface:

dy/dx=-e^-x2sin2X-e^xsin2x

d^2y/dx^2= -e^x2sin2X+4e^-xsin2x+sinx

arghhhh help! :redface:
Reply 1
Original post by -Illmatic-
Given that y=e^-x.cosx, show that d^2y/dx^2+2(dy/dx)+2y=0

Absolute pain in the backside...I got as far differentiating and then differentiating again so I'm left with the mess of tidying it up :redface:

dy/dx=-e^-x2sin2X-e^xsin2x

d^2y/dx^2= -e^x2sin2X+4e^-xsin2x+sinx

arghhhh help! :redface:


Is that (e^-x)cosx 0r e^(-x.cosx)
Reply 2
Original post by steve2005
Is that (e^-x)cosx 0r e^(-x.cosx)


the former: (e^-x)cosx
Reply 3
Your dy/dx is wrong.
Reply 4
Original post by steve2005
Is that (e^-x)cosx 0r e^(-x.cosx)


I think it's (e^-x)*(cosx) .
(edited 12 years ago)
Original post by -Illmatic-
Given that y=e^-x.cosx, show that d^2y/dx^2+2(dy/dx)+2y=0

Absolute pain in the backside...I got as far differentiating and then differentiating again so I'm left with the mess of tidying it up :redface:

dy/dx=-e^-x2sin2X-e^xsin2x

d^2y/dx^2= -e^x2sin2X+4e^-xsin2x+sinx

arghhhh help! :redface:

k this shouldn't be difficult.

the only difficulty is keeping everything tidy.

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