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X^2+4x-21=0 Solve for x

Quadractics factorise into double brackets like (x-a)(x-b). We ave to find the facors of -21 which add to make +4. 7 and -3 suffice. (x-3)(x+7) Then x will be equal to 3 and -7 for the equation.

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X^2+4x-21=0 Solve for x

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