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Myr73
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Let u and v be vectors in R^n , and let T be a linear operator on R^n. Prove that T(u).T(v)= u.v if and only if A^T=A^-1 where A is the standard matrix for T. What I have so far is --> If T is a linear operator on R^n, then ; T:R^n --> R^n
and if u and v be the vectors then ; T(u).T(V) = Au.Av
Where A is the standard matrix of T
{ and so we want Au.Av=u.v, which needs to be if and only if A^T=A^-1}
Therefore first we find what it means if A^T=A^-1
----> if A^T=A^-1 then multiplying both by A --> AA^T= I
Therefore the matrix A is and orthogonal matrix/
And so from the last statement , if Au.Av= u.v if and only if A^T=A^-1
Then --> Au.Av=u.v if and only if A is an orthogonal matrix.
Therefore we must prove that Au.Av= u.v means that this is only true if the matrix A is orthogonal.
This is where I am stuck I'm not sure how to prove this.
I'm not sure if this next part is necessary but I found that
u.v = u1v1+u2v2...UnVn
and that T(u)=A(u) such that a(11)u(1), a(12)u(2),..,a(1n)u(1)
a(21)u(1), a(22)u(2)...,a(2n)u(2)
..........
.........
a(n1)u(1), a(n2)u(2)...a(nn)u(n)
and same for T(v)=A(v) such that
a(11)v(1), a(12)v(2),..,a(1n)v(1)
a(21)v(1), a(22)v(2)...,a(2n)v(2)
..........
.........
a(n1)v(1), a(n2)v(2)...a(nn)v(n)
Im not sure if I need to develop T(u).T(v) further then A(u).A(v)..
I would really appreciate some help on this one, thanks
and if u and v be the vectors then ; T(u).T(V) = Au.Av
Where A is the standard matrix of T
{ and so we want Au.Av=u.v, which needs to be if and only if A^T=A^-1}
Therefore first we find what it means if A^T=A^-1
----> if A^T=A^-1 then multiplying both by A --> AA^T= I
Therefore the matrix A is and orthogonal matrix/
And so from the last statement , if Au.Av= u.v if and only if A^T=A^-1
Then --> Au.Av=u.v if and only if A is an orthogonal matrix.
Therefore we must prove that Au.Av= u.v means that this is only true if the matrix A is orthogonal.
This is where I am stuck I'm not sure how to prove this.
I'm not sure if this next part is necessary but I found that
u.v = u1v1+u2v2...UnVn
and that T(u)=A(u) such that a(11)u(1), a(12)u(2),..,a(1n)u(1)
a(21)u(1), a(22)u(2)...,a(2n)u(2)
..........
.........
a(n1)u(1), a(n2)u(2)...a(nn)u(n)
and same for T(v)=A(v) such that
a(11)v(1), a(12)v(2),..,a(1n)v(1)
a(21)v(1), a(22)v(2)...,a(2n)v(2)
..........
.........
a(n1)v(1), a(n2)v(2)...a(nn)v(n)
Im not sure if I need to develop T(u).T(v) further then A(u).A(v)..
I would really appreciate some help on this one, thanks