Q. Expand -            
(3x - 5y - 2z)(3x - 5y + 2z)

Dear Student,

$$\begin{gathered} \left(3x - 5y - 2z\right)\left(3x - 5y + 2z\right) \\ = 3x\left(3x - 5y + 2z\right) - 5y\left(3x - 5y + 2z\right) - 2z\left(3x - 5y + 2z\right) \\ = 9x^2 - 15xy + \cancel{6xz} - 15xy + 25y^2 - \cancel{10yz} - \cancel{6xz} + \cancel{10yz} - 4z^2 \\ = \boxed{\mathbf{9}{\mathbf{x}}^{\mathbf{2}}\mathbf{ }\mathbf{+}\mathbf{ }\mathbf{25}{\mathbf{y}}^{\mathbf{2}}\mathbf{ }\mathbf{-}\mathbf{ }\mathbf{4}{\mathbf{z}}^{\mathbf{2}}\mathbf{ }\mathbf{-}\mathbf{ }\mathbf{30}\mathbf{x}\mathbf{y}} \end{gathered}$$

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