factorise `(a^2-3a)(a^2-3a+7)+10`

Explanation

Let `a^2-3a = x`

Then, our polynomial becomes,

`x(x+7)+10`

`=x^2+7x+10`

`=x^2+5x+2x+10`

`=(x+5)(x+2)`

`=(a^2-3a+5)(a^2-3a+2)`

Now, `a^2-3a+5` will have no factor as discriminant is `-11` that is less than `0`.

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