- #1
coldturkey
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Consider 2nd order differential equation:
[itex]
a_{2}y''(x) + a_{1}y'(x) + a_{0}y(x) = 0
[/itex]
Let b and c be the roots of the quadratic [itex]a_{2}x^2 + a_{1}x + a_{0}[/itex]
Verify that when b = c then [itex]xe^{bx}[/itex] is a solution of the Differential equation.
-----------------------------
Ok so I differentiate y a couple times and get
[itex]
y = xe^{bx}
[/itex]
[itex]
y' = xbe^{bx} + e^{bx}
[/itex]
[itex]
y'' = xb^2e^{bx}+2be^{bx}
[/itex]
Substituting into the equation yields:
[itex]
a_{2}(xb^2e^{bx}+2be^{bx}) + a_{1}(xbe^{bx} + e^{bx}) + a_{0}(xe^{bx}) = 0
[/itex]
Now if I rearrange the quadratic equation for a0
[itex]
a_{0} = -a_{2}b^2 - a_{1}b
[/itex]
then substituting that in I get
[itex]
a_{2}(xb^2e^{bx}+2be^{bx}) + a_{1}(xbe^{bx} + e^{bx}) + (-a_{2}b^2 - a_{1}b)(xe^{bx}) = 0
[/itex]
[itex]
= a_{2}2be^{bx} + a_{1}e^{bx} = 0
[/itex]
This is where I get stuck, there must be something I've missed which I can use to further simplify. I did the proof for [itex]y = e^{bx}[/itex] in the same way and it worked out easy. Can anybody give me a hint on what to do next? thanks
[itex]
a_{2}y''(x) + a_{1}y'(x) + a_{0}y(x) = 0
[/itex]
Let b and c be the roots of the quadratic [itex]a_{2}x^2 + a_{1}x + a_{0}[/itex]
Verify that when b = c then [itex]xe^{bx}[/itex] is a solution of the Differential equation.
-----------------------------
Ok so I differentiate y a couple times and get
[itex]
y = xe^{bx}
[/itex]
[itex]
y' = xbe^{bx} + e^{bx}
[/itex]
[itex]
y'' = xb^2e^{bx}+2be^{bx}
[/itex]
Substituting into the equation yields:
[itex]
a_{2}(xb^2e^{bx}+2be^{bx}) + a_{1}(xbe^{bx} + e^{bx}) + a_{0}(xe^{bx}) = 0
[/itex]
Now if I rearrange the quadratic equation for a0
[itex]
a_{0} = -a_{2}b^2 - a_{1}b
[/itex]
then substituting that in I get
[itex]
a_{2}(xb^2e^{bx}+2be^{bx}) + a_{1}(xbe^{bx} + e^{bx}) + (-a_{2}b^2 - a_{1}b)(xe^{bx}) = 0
[/itex]
[itex]
= a_{2}2be^{bx} + a_{1}e^{bx} = 0
[/itex]
This is where I get stuck, there must be something I've missed which I can use to further simplify. I did the proof for [itex]y = e^{bx}[/itex] in the same way and it worked out easy. Can anybody give me a hint on what to do next? thanks
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