Proofs from Existence, uniqueness and linear operators
All proofs from Existence, uniqueness and linear operators.
[PROOF]If yh∈ker(T), then
T[yp+yh]=T[yp]+T[yh]=f+0=f,so every element of yp+ker(T) is a solution. Conversely, if y is any solution of T[y]=f, then
T[y−yp]=T[y]−T[yp]=f−f=0.Thus y−yp∈ker(T), so y=yp+yh for some yh∈ker(T).