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MATH
[1251]

Proofs from Existence, uniqueness and linear operators

All proofs from Existence, uniqueness and linear operators.

If yh∈ker⁡(T)y_h\in\ker(T), then

T[yp+yh]=T[yp]+T[yh]=f+0=f,T[y_p+y_h]=T[y_p]+T[y_h]=f+0=f,

so every element of yp+ker⁡(T)y_p+\ker(T) is a solution. Conversely, if yy is any solution of T[y]=fT[y]=f, then

T[y−yp]=T[y]−T[yp]=f−f=0.T[y-y_p]=T[y]-T[y_p]=f-f=0.

Thus y−yp∈ker⁡(T)y-y_p\in\ker(T), so y=yp+yhy=y_p+y_h for some yh∈ker⁡(T)y_h\in\ker(T).