Suppose the 2 × 2 matrix A has eigenvalues λ1 = 4 and λ2 = 3, with eigenvectors v1 and v2, respectively. If u = 5v1 + v2, then A 2u is equal to

(a) 25v1 + v2
(b) 25v1 + 3v2
(c) 80v1 + 9v2
(d) 100v1 + 3v2
(e) 400v1 + 9v2

Respuesta :

[tex]A^{2} u is equal to 80 v_{1}+9 v_{2}[/tex]

Answer: Option C

Step-by-step explanation:

Given A is [tex]2 \times 2[/tex] matrix has Eigen values [tex]\lambda_{1}=4[/tex] and \lambda_{2}=3 with Eigen vectors [tex]v_{1} \text { and } v_{2}[/tex] respectively.

[tex]\lambda_{1}=4[/tex] and [tex]v_{1}[/tex]  is the eigen vector, substitute this to A so then

                  [tex]A v_{1}=\lambda_{1} v_{1}=4 v_{1}[/tex]

Squaring ‘A’ value ‘4’, we get

                [tex]A^{2} v_{1}=16 v_{1}[/tex]

Given [tex]u=5 v_{1}+v_{2}[/tex], from this, the above can be written as

                [tex]A^{2}\left(5 v_{1}\right)=5 A^{2} v_{1}=5 \times 16 v_{1}=80 v_{1}[/tex]

Similarly, [tex]\lambda_{2}=3[/tex] and [tex]v_{2}[/tex] is the eigen vector. Then,

                [tex]A v_{2}=\lambda_{2} v_{2}=3 \times v_{2}[/tex]

Squaring ‘A’ value ‘3’, we get

               [tex]A^{2} v_{2}=9 \times v_{2}[/tex]

To find [tex]A^{2} u[/tex], multiply [tex]A^{2}[/tex] in both sides of the equation [tex]u=5 v_{1}+v_{2}[/tex], we get

              [tex]A^{2} u=A^{2} \times\left(5 v_{1}+v_{2}\right)[/tex]

              [tex]A^{2} u=5 A^{2} v_{1}+A^{2} v_{2}[/tex]

Substitute the value that found above,

             [tex]A^{2} u=80 v_{1}+9 v_{2}[/tex]