Question

Using proper identities, expand the following


$\mathbf{\left(}\mathit{i}\mathit{i}\mathbf{\right)}\mathbf{}\left(3x+y-5\right)\left(3x-y-5\right)$

Answer 1

Dear student
$$\begin{gathered} \mathrm{We}\mathrm{have} \\ \left(3\mathrm{x}+\mathrm{y}-5\right)\left(3\mathrm{x}-\mathrm{y}-5\right) \\ 3x\left(3\mathrm{x}-\mathrm{y}-5\right)+y\left(3\mathrm{x}-\mathrm{y}-5\right)-5\left(3\mathrm{x}-\mathrm{y}-5\right) \\ =9x^2-\cancel{3xy}-15x+\cancel{3xy}-y^2-\cancel{5y}-15x+\cancel{5y}+25 \\ =9x-y^2-30x+25 \end{gathered}$$
Regards