Question

$( {x}^{2} - 4x - 21 \:$
factorise
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Answer 1

Answer:

${x}^{2} - 4x - 21$

We will do it by splitting middle term in two numbers so that when both multiplied the last number means -21( in this question) will be the result and when we add that then the middle number -4x(in this question comes.

${x}^{2} + 7x - 3x - 21$

$x( x + 7) - 3(x + 7)$

$(x - 3)(x + 7)$