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The inverse of matrix N = [[2, 3], [1, 4]] is

Mathematics

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Answer

15(4−3−12)\dfrac{1}{5}\begin{pmatrix}4&-3\\-1&2\end{pmatrix}

Step-by-step solution

3 steps
  1. Compute the determinant of N=(2314)N = \begin{pmatrix} 2 & 3 \\ 1 & 4 \end{pmatrix}.

    det⁡(N)=∣2314∣=2⋅4−3⋅1=8−3=5\det(N) = \begin{vmatrix} 2 & 3 \\ 1 & 4 \end{vmatrix} = 2 \cdot 4 - 3 \cdot 1 = 8 - 3 = 5

    Since det⁡(N)=5≠0\det(N) = 5 \neq 0, the inverse exists.

  2. Apply the formula for the inverse of a 2×22 \times 2 matrix (abcd)\begin{pmatrix} a & b \\ c & d \end{pmatrix}

    (abcd)−1=1ad−bc(d−b−ca)\begin{pmatrix} a & b \\ c & d \end{pmatrix}^{-1} = \frac{1}{ad - bc} \begin{pmatrix} d & -b \\ -c & a \end{pmatrix}

    Substitute a=2a=2, b=3b=3, c=1c=1, d=4d=4, det⁡(N)=5\det(N)=5:

    N−1=15(4−3−12)N^{-1} = \frac{1}{5} \begin{pmatrix} 4 & -3 \\ -1 & 2 \end{pmatrix}
  3. Verify by computing N⋅N−1N \cdot N^{-1}.

    First row, first column: 2⋅45+3⋅−15=85−35=55=12 \cdot \frac{4}{5} + 3 \cdot \frac{-1}{5} = \frac{8}{5} - \frac{3}{5} = \frac{5}{5} = 1

    First row, second column: 2⋅−35+3⋅25=−65+65=05=02 \cdot \frac{-3}{5} + 3 \cdot \frac{2}{5} = \frac{-6}{5} + \frac{6}{5} = \frac{0}{5} = 0

    Second row, first column: 1⋅45+4⋅−15=45−45=05=01 \cdot \frac{4}{5} + 4 \cdot \frac{-1}{5} = \frac{4}{5} - \frac{4}{5} = \frac{0}{5} = 0

    Second row, second column: 1⋅−35+4⋅25=−35+85=55=11 \cdot \frac{-3}{5} + 4 \cdot \frac{2}{5} = \frac{-3}{5} + \frac{8}{5} = \frac{5}{5} = 1

    N⋅N−1=(1001)=IN \cdot N^{-1} = \begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix} = I

    15(4−3−12)\boxed{\dfrac{1}{5}\begin{pmatrix}4&-3\\-1&2\end{pmatrix}}

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