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Mathematics

Find x and y, if :

[3x8][1437]3[27]=5[32y]\begin{bmatrix}[r] 3x & 8 \end{bmatrix}\begin{bmatrix}[r] 1 & 4 \ 3 & 7 \end{bmatrix} - 3\begin{bmatrix}[r] 2 & -7 \end{bmatrix} = 5\begin{bmatrix}[r] 3 & 2y \end{bmatrix}

Matrices

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Answer

Given,

[3x×1+8×33x×4+8×7][621]=[1510y][3x+2412x+56][621]=[1510y][3x+24612x+56(21)]=[1510y][3x+1812x+77]=[1510y]\Rightarrow \begin{bmatrix}[r] 3x \times 1 + 8 \times 3 & 3x \times 4 + 8 \times 7 \end{bmatrix} - \begin{bmatrix}[r] 6 & -21 \end{bmatrix} = \begin{bmatrix}[r] 15 & 10y \end{bmatrix} \\[1em] \Rightarrow \begin{bmatrix}[r] 3x + 24 & 12x + 56 \end{bmatrix} - \begin{bmatrix}[r] 6 & -21 \end{bmatrix} = \begin{bmatrix}[r] 15 & 10y \end{bmatrix} \\[1em] \Rightarrow \begin{bmatrix}[r] 3x + 24 - 6 & 12x + 56 - (-21) \end{bmatrix} = \begin{bmatrix}[r] 15 & 10y \end{bmatrix} \\[1em] \Rightarrow \begin{bmatrix}[r] 3x + 18 & 12x + 77 \end{bmatrix} = \begin{bmatrix}[r] 15 & 10y \end{bmatrix}

By definition of equality of matrices we get,

3x + 18 = 15
⇒ 3x = -3
⇒ x = -1.

12x + 77 = 10y
⇒ 12(-1) + 77 = 10y
⇒ 65 = 10y
⇒ y = 6.5

Hence, x = -1 and y = 6.5

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