To factorise an equation like this we must first make the equation equal to 0 therefore it becomes: x^2+10x+21.Now we have the equation in a way that we can work with it we can factorise.To do this we need to find 2 numbers that add to make 10 and times to make 21.3 and 7 both add to make 10 and times to make 21 therefore the factorised equation:x^2+10x+21 = (x+3)(x+7) = 0now we have the equation factorised we can solve it. to solve it we need to make x equal a number that will make each bracket = 0 as any number times 0 equals 0.if we sub in x = -3: (-3 +3) *(-3 +7) = 0, 0 * 4 = 0 therefore x =-3if we sub in x = -7: (-7 +3) ( -7 +7) =0, -4 * 0 = 0 therefore x = -7our answer to the question x=-3 and x=-7

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