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PsychonautQQ
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Homework Statement
Let P be the vector space of one variable polynomials with complex coefficients. if D: P-->P is the derivative mapping, show that the linear mapping D^2+2D+I is invertible.
Homework Equations
show that D^2+2D+I is both injective and surjective
The Attempt at a Solution
Showing injectivity: assume D^2+2D+I(u)=D^2+2D+I(v), we want to show that this implies that u=v.
D^2+2D+I(u)=D^2+2D+I(v)
(D+I)^2(u) = (D+I)^2(v)
(D+I)(D+I)(u) = (D+I)(D+I)(v)
Since D and I are both given as linear mappings, we know D+I is linear, so (D+I)(D+I)(u) = (D+I)(u)(D+I)(u) = (D+I)(v)(D+I)(v)
And now I'm kind of lost... Am I on the right track with showing injectivity?
edit: Maybe I would have better luck with showing injectivity by showing that the Ker(D^2+2D+I) = {0}? Would this involve solving an ODE? Ahh somebody help me I'm so confused ;-(.
Surjective: We want to show that if u is an element of P, then there exists a v in P such that (D^2+2D+I)(v) = u. I have no idea how to show this one. Anyone got any tips to offer?
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