Question

factorise 7 x-2y
factorise
${m}^{2} + 17mn - 84 { n}^{2}$

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Answer 1

Please use $(x+a)+(x+b)=x^2+(a+b)x+ab$.

$m^2+17mn-84n^2$

We know the sum and multiplication of $21n$ and $-4n$ :

sum is $17n$ and multiplication is $-84n^2$.

Now I'll use it.

∴ $m^2+17mn-84n^2=(m+21n)(m-4n)$