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Given the matrix A = i & 0 0 & -i .

Mathematics

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Answer

A4=I2A^4 = I_2

Step-by-step solution

3 steps

To show that A4=I2A^4 = I_2, we first need to calculate A2A^2 and then A4A^4.
Given the matrix A=[i00−i]A = \begin{bmatrix} i & 0 \\ 0 & -i \end{bmatrix}.
Recall that i2=−1i^2 = -1.

  1. Calculate A2A^2

    A2=A×AA^2 = A \times A A2=[i00−i]×[i00−i]A^2 = \begin{bmatrix} i & 0 \\ 0 & -i \end{bmatrix} \times \begin{bmatrix} i & 0 \\ 0 & -i \end{bmatrix}

    Perform matrix multiplication:

    A2=[(i)(i)+(0)(0)(i)(0)+(0)(−i)(0)(i)+(−i)(0)(0)(0)+(−i)(−i)]A^2 = \begin{bmatrix} (i)(i) + (0)(0) & (i)(0) + (0)(-i) \\ (0)(i) + (-i)(0) & (0)(0) + (-i)(-i) \end{bmatrix} A2=[i2+00+00+00+(−i)2]A^2 = \begin{bmatrix} i^2 + 0 & 0 + 0 \\ 0 + 0 & 0 + (-i)^2 \end{bmatrix}

    Since i2=−1i^2 = -1 and (−i)2=(−1)2i2=1⋅(−1)=−1(-i)^2 = (-1)^2 i^2 = 1 \cdot (-1) = -1:

    A2=[−100−1]A^2 = \begin{bmatrix} -1 & 0 \\ 0 & -1 \end{bmatrix}
  2. Calculate A4A^4

    We can calculate A4A^4 as A2×A2A^2 \times A^2.

    A4=[−100−1]×[−100−1]A^4 = \begin{bmatrix} -1 & 0 \\ 0 & -1 \end{bmatrix} \times \begin{bmatrix} -1 & 0 \\ 0 & -1 \end{bmatrix}

    Perform matrix multiplication:

    A4=[(−1)(−1)+(0)(0)(−1)(0)+(0)(−1)(0)(−1)+(−1)(0)(0)(0)+(−1)(−1)]A^4 = \begin{bmatrix} (-1)(-1) + (0)(0) & (-1)(0) + (0)(-1) \\ (0)(-1) + (-1)(0) & (0)(0) + (-1)(-1) \end{bmatrix} A4=[1+00+00+00+1]A^4 = \begin{bmatrix} 1 + 0 & 0 + 0 \\ 0 + 0 & 0 + 1 \end{bmatrix} A4=[1001]A^4 = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}
  3. Compare with I2I_2

    The identity matrix of order 2 is I2=[1001]I_2 = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}.
    Since A4=[1001]A^4 = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}, we have A4=I2A^4 = I_2.

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