Let A be a matrix, and let x and y be linearly independent vectors such that Ax=y, Ay=x+2y.Then we have that A^5 x=ax+by for some scalars a and b. Find the ordered pair (a, b).

Camila Brandt

Camila Brandt

Answered question

2022-09-27

Let A be a matrix, and let 𝐱 and 𝐲 be linearly independent vectors such that 𝐀𝐱=𝐲,𝐀𝐲=𝐱+2𝐲.Then we have that A 5 x = a x + b y for some scalars 𝑎 and 𝑏. Find the ordered pair (a, b).
So far I have A 5 x = A 4 y
A 4 y = A 3 x + 2 A 3 y

Answer & Explanation

Miya Swanson

Miya Swanson

Beginner2022-09-28Added 11 answers

You were on the right track. Here are the next steps.
A 3 x = A 2 y and 2 A 3 y = 2 A 2 ( x + 2 y )
A 2 y = A A y = A ( x + 2 y ) and 2 A A x + 4 A A y = 2 A y + 4 A ( x + 2 y )
Can you take it from here?
Jase Rocha

Jase Rocha

Beginner2022-09-29Added 2 answers

You are trying to reduce the powers, which works if you keep going. You can increase them as well. If A x = y and A y = x + 2 y, then
A 2 x = A ( A x ) = A y = x + 2 y A 2 y = A ( x + 2 y ) = A x + 2 A y = y + 2 ( x + 2 y ) = 2 x + 5 y A 3 x = A 2 y = 2 x + 5 y A 4 x = A 3 y = A ( 2 x + 5 y ) = 2 y + 5 ( x + 2 y ) = 5 x + 12 y

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