To find the matrix M(T) of the linear transformation T: V → V with respect to the basis β = {x₁, x₂}, given the matrix M(T) with respect to the basis β' = {y₁, y₂}, we need to express the basis vectors x₁ and x₂ in terms of y₁ and y₂, and then use the change of basis formula.
Given:
- V is a two-dimensional vector space over R
- T: V → V is a linear map
- β = {x₁, x₂} is a basis for V
- β' = {y₁, y₂} is another basis for V, where y₁ = x₁ and y₂ = x₁ + x₂
- M(T) with respect to β' is, by rows, [2 -1], [3 1]
Step 1: Express x₁ and x₂ in terms of y₁ and y₂.
Since y₁ = x₁, we have:
x₁ = y₁
Since y₂ = x₁ + x₂, we can rearrange to get:
x₂ = y₂ - x₁
= y₂ - y₁
Step 2: Construct the transition matrix P from β' to β.
The transition matrix P represents the change of basis from β' to β, and its columns are the coordinate vectors of the basis vectors of β with respect to β'.
P = [
[ 1, 0 ], # Coordinate vector of x₁ with respect to β'
[ 1, 1 ] # Coordinate vector of x₂ with respect to β'
]
Step 3: Find the matrix M(T) with respect to β using the change of basis formula.
M(T)_β = P⁻¹ × M(T)_β' × P
Where:
- M(T)_β is the matrix of T with respect to the basis β
- M(T)_β' is the given matrix of T with respect to the basis β'
- P is the transition matrix from β' to β
- P⁻¹ is the inverse of P
First, we need to find P⁻¹:
P⁻¹ = [
[ 1, -1 ],
[ 0, 1 ]
]
Now, we can calculate M(T)_β:
M(T)_β = P⁻¹ × M(T)_β' × P
= [
[ 1, -1 ],
[ 0, 1 ]
] × [
[ 2, -1 ],
[ 3, 1 ]
] × [
[ 1, 0 ],
[ 1, 1 ]
]
= [
[ 2, 1 ],
[ 3, 0 ]
]
Therefore, the matrix M(T) of the linear transformation T: V → V with respect to the basis β = {x₁, x₂} is:
M(T)_β = [
[ 2, 1 ],
[ 3, 0 ]
]