Skip to main contentSkip to solution

If A=[1101]A = \begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix}, then the value of A20A^{20} is:

Solution

Correct Option: 3

Given A=[1101]A = \begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix}

Calculate A2A^2:

A2=A×AA^2 = A \times A

=[1101]×[1101]= \begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix} \times \begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix}

=[1201]= \begin{bmatrix} 1 & 2 \\ 0 & 1 \end{bmatrix}


Calculate A3A^3:

A3=A2×AA^3 = A^2 \times A

=[1201]×[1101]= \begin{bmatrix} 1 & 2 \\ 0 & 1 \end{bmatrix} \times \begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix}

=[1301]= \begin{bmatrix} 1 & 3 \\ 0 & 1 \end{bmatrix}


The pattern emerges:

A1=[1101]A^1 = \begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix}

A2=[1201]A^2 = \begin{bmatrix} 1 & 2 \\ 0 & 1 \end{bmatrix}

A3=[1301]A^3 = \begin{bmatrix} 1 & 3 \\ 0 & 1 \end{bmatrix}

The general form is An=[1n01]A^n = \begin{bmatrix} 1 & n \\ 0 & 1 \end{bmatrix}


For n=20n = 20:

A20=[12001]A^{20} = \begin{bmatrix} 1 & 20 \\ 0 & 1 \end{bmatrix}

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question