Subjects Linear Algebra

Matrix Addition

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Matrix Addition


1. **State the problem:** We are given two 3x3 matrices A and B: $$A = \begin{pmatrix}7 & 8 & 6 \\ 1 & 3 & 9 \\ -4 & 3 & -1\end{pmatrix}, \quad B = \begin{pmatrix}4 & 11 & -3 \\ -1 & 2 & 4 \\ 7 & 5 & 0\end{pmatrix}$$ We need to find the matrix $2A + B$. 2. **Multiply matrix A by scalar 2:** Multiply every element of A by 2: $$2A = 2 \times \begin{pmatrix}7 & 8 & 6 \\ 1 & 3 & 9 \\ -4 & 3 & -1\end{pmatrix} = \begin{pmatrix}14 & 16 & 12 \\ 2 & 6 & 18 \\ -8 & 6 & -2\end{pmatrix}$$ 3. **Add matrices $2A$ and $B$ element-wise:** $$2A + B = \begin{pmatrix}14 & 16 & 12 \\ 2 & 6 & 18 \\ -8 & 6 & -2\end{pmatrix} + \begin{pmatrix}4 & 11 & -3 \\ -1 & 2 & 4 \\ 7 & 5 & 0\end{pmatrix} = \begin{pmatrix}14+4 & 16+11 & 12 + (-3) \\ 2 + (-1) & 6 + 2 & 18 + 4 \\ -8 + 7 & 6 + 5 & -2 + 0\end{pmatrix} = \begin{pmatrix}18 & 27 & 9 \\ 1 & 8 & 22 \\ -1 & 11 & -2\end{pmatrix}$$ 4. **Final answer:** $$\boxed{\begin{pmatrix}18 & 27 & 9 \\ 1 & 8 & 22 \\ -1 & 11 & -2\end{pmatrix}}$$ This matrix is the result of $2A + B$.