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D=[[4,-1],[2,-1]] and

A=[[3,1,0],[2,1,-2]]
Let 
H=DA. Find 
H.

H=

D=[4amp;12amp;1] \mathrm{D}=\left[\begin{array}{ll}4 & -1 \\ 2 & -1\end{array}\right] and A=[3amp;1amp;02amp;1amp;2] A=\left[\begin{array}{rrr} 3 & 1 & 0 \\ 2 & 1 & -2 \end{array}\right] \newlineLet H=DA \mathrm{H}=\mathrm{DA} . Find H \mathrm{H} .\newlineH= \mathbf{H}=

Full solution

Q. D=[4121] \mathrm{D}=\left[\begin{array}{ll}4 & -1 \\ 2 & -1\end{array}\right] and A=[310212] A=\left[\begin{array}{rrr} 3 & 1 & 0 \\ 2 & 1 & -2 \end{array}\right] \newlineLet H=DA \mathrm{H}=\mathrm{DA} . Find H \mathrm{H} .\newlineH= \mathbf{H}=
  1. Understand matrix multiplication rules: Understand matrix multiplication rules.\newlineTo multiply two matrices, the number of columns in the first matrix must equal the number of rows in the second matrix. The resulting matrix will have the same number of rows as the first matrix and the same number of columns as the second matrix.
  2. Verify matrix multiplication possibility: Verify if matrix multiplication is possible. Matrix DD is a 2×22 \times 2 matrix and matrix AA is a 2×32 \times 3 matrix. Since the number of columns in DD (22) equals the number of rows in AA (22), matrix multiplication is possible.
  3. Set up the multiplication: Set up the multiplication.\newlineTo multiply DD by AA, we take each row of DD and multiply it by each column of AA, summing the products to get the entries of the resulting matrix HH.
  4. Calculate first entry of matrix HH: Calculate the first entry of matrix HH. Multiply the first row of DD by the first column of AA and sum the products. H[1,1]=(4×3)+(1×2)=122=10H[1,1] = (4 \times 3) + (-1 \times 2) = 12 - 2 = 10
  5. Calculate second entry of first row of matrix HH: Calculate the second entry of the first row of matrix HH. Multiply the first row of DD by the second column of AA and sum the products. H[1,2]=(4×1)+(1×1)=41=3H[1,2] = (4 \times 1) + (-1 \times 1) = 4 - 1 = 3
  6. Calculate third entry of first row of matrix HH: Calculate the third entry of the first row of matrix HH. Multiply the first row of DD by the third column of AA and sum the products. H[1,3]=(4×0)+(1×2)=0+2=2H[1,3] = (4 \times 0) + (-1 \times -2) = 0 + 2 = 2
  7. Calculate first entry of second row of matrix HH: Calculate the first entry of the second row of matrix HH. Multiply the second row of DD by the first column of AA and sum the products. H[2,1]=(2×3)+(1×2)=62=4H[2,1] = (2 \times 3) + (-1 \times 2) = 6 - 2 = 4
  8. Calculate second entry of second row of matrix HH: Calculate the second entry of the second row of matrix HH. Multiply the second row of DD by the second column of AA and sum the products. H[2,2]=(2×1)+(1×1)=21=1H[2,2] = (2 \times 1) + (-1 \times 1) = 2 - 1 = 1
  9. Calculate third entry of second row of matrix HH: Calculate the third entry of the second row of matrix HH. Multiply the second row of DD by the third column of AA and sum the products. H2,3=(2×0)+(1×2)=0+2=2H_{2,3} = (2 \times 0) + (-1 \times -2) = 0 + 2 = 2
  10. Combine entries to form matrix H: Combine all the entries to form matrix HH.H=[10amp;3amp;2 4amp;1amp;2]H = \left[\begin{array}{ccc}10 & 3 & 2 \ 4 & 1 & 2\end{array}\right]

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