# Homework Help: No idea where to start for linear transformation question from P2->P2

1. Jul 22, 2011

### jra0718

Let T:P2$\rightarrow$P2 be given by

T(x-1)=1-x
T(x2-2x)=-1+x-2x2
T(3-x2)=-1+2x+3x2

Find the matrix for T with respect to the standard basis B={1,x,x2}for P2

To be honest, I have no idea where to start. Help would be greatly appreciated

2. Jul 23, 2011

### ehild

Write the polynomials as column vectors like
x-1 --->
-1,
1
0
x^2-2x --->
0
-2
1

and so on and make a matrix A from the three columns on the left hand side of the equation and a matrix B from the columns at the right-hand side. You get a matrix equation TA=B which you can solve for T
by multiplying both sides with the inverse of A:
T=TA A-1=BA-1.

ehild

3. Jul 23, 2011

### jra0718

i dont understand how you got the column vectors

4. Jul 23, 2011

### ehild

1, x, x^2 are the basis, consider them as base vectors e1, e2, e3. The coefficient of x^k in the polynomial is considered as the k-th component.

For example, -1+x-2x^2 = -1 (1) +1 (x) -2 (x^2) or -1 e1 +1*e2 -2 e3. You can write it as the vector (-1,1,-2), or its transposed as column vector.

ehild

Last edited: Jul 23, 2011