i have a doubt on the 3 question please explain the method clearly

Dear Student,

$$\begin{gathered} \mathrm{Q}3. \left(\mathrm{e}\right) {\mathrm{c}}^2-6\mathrm{c}+9-{\mathrm{y}}^2 \\ = {\mathrm{c}}^2-2\times 3\times \mathrm{c}+{\left(3\right)}^2-{\mathrm{y}}^2 \\ [\mathrm{Using} {\left(a-b\right)}^2= a^2+b^2-2\mathrm{ab}] \\ = {\left(\mathrm{c}-3\right)}^2-{\mathrm{y}}^2 \\ [\mathrm{Using} a^2-b^2 = \left(a-b\right)\left(a+b\right)] \\ (c-3-y)(c-3+y) \end{gathered}$$

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