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Prove the Following Identities: ∣ ∣ ∣ ∣ 2 Y Y − Z − X 2 Y 2 Z 2 Z Z − X − Y X − Y − Z 2 X 2 X ∣ ∣ ∣ ∣ = ( X + Y + Z ) 3 - Mathematics

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प्रश्न

Prove the following identity:

\[\begin{vmatrix}2y & y - z - x & 2y \\ 2z & 2z & z - x - y \\ x - y - z & 2x & 2x\end{vmatrix} = \left( x + y + z \right)^3\]

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उत्तर

\[LHS\]

\[ = \begin{vmatrix}2y & y - z - x & 2y \\ 2z & 2z & z - x - y \\ x - y - z & 2x & 2x\end{vmatrix}\]

\[ = \begin{vmatrix}2y + 2z + x - y - z & y - z - x + 2z + 2x & 2y + z - x - y + 2x \\ 2z & 2z & z - x - y \\ x - y - z & 2x & 2x\end{vmatrix} \left[\text{ Applying }R_1 \text{ to }R_1 + R_2 + R_3 \right]\]

\[ = \begin{vmatrix}x + y + z & x + y + z & x + y + z \\ 2z & 2z & z - x - y \\ x - y - z & 2x & 2x\end{vmatrix}\]

\[ = \left( x + y + z \right)\begin{vmatrix}1 & 1 & 1 \\ 2z & 2z & z - x - y \\ x - y - z & 2x & 2x\end{vmatrix} \left[\text{ Taking }\left( x + y + z \right)\text{ common from }R_1 \right]\]

\[ = \left( x + y + z \right)\begin{vmatrix}0 & 1 & 1 \\ 0 & 2z & z - x - y \\ - x - y - z & 2x & 2x\end{vmatrix} \left[\text{ Applying }C_1 \text{ to }C_1 - C_2 \right]\]

\[ = \left( x + y + z \right)^2 \begin{vmatrix}0 & 1 & 1 \\ 0 & 2z & z - x - y \\ - 1 & 2x & 2x\end{vmatrix} \left[\text{ Taking }\left( x + y + z \right)\text{ common from }C_1 \right]\]

\[ = \left( x + y + z \right)^2 \left[ - 1\left( z - x - y - 2z \right) \right] \left[\text{ Expanding along first column }\right]\]

\[ = \left( x + y + z \right)^3 \]

\[ = RHS\]

\[ \therefore \begin{vmatrix}2y & y - z - x & 2y \\ 2z & 2z & z - x - y \\ x - y - z & 2x & 2x\end{vmatrix} = \left( x + y + z \right)^3\]

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पाठ 6: Determinants - Exercise 6.2 [पृष्ठ ६१]

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आरडी शर्मा Mathematics [English] Class 12
पाठ 6 Determinants
Exercise 6.2 | Q 42 | पृष्ठ ६१

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