We are studying polynomials
(x+3)(x-7)=0
2x^2+3x-9=0
5x^2+2x=0
x = - 3 or x = 7 makes the left zero.
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factors of 2 are 1 and 2
factors of 9 are 1, 9, 3
need combination that differs by 3
well 2 * 3 and 3 will work
(2 x - 3) (x+3) = 0
x = 3/2 or x = -3 makes the left zero
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now really try them first yourself
x (5 x + 2) = 0
x = 0 or x = -2/5 makes it zero