solve the following equations by factorization

(1)
x^2-4x-21 = 0
(x-7)(x+3) = 0
x-7 = 0 or x+3 = 0
x = 7 or x = -3

(2)
2x^2-13x+20=0
(2x-5)(x-4)=0
2x-5 = 0 or x-4 = 0
x = 5/2 or x = 4

(3)
4x^2+12x+9=0
(2x+3)(2x+3)=0
(2x+3)^2=0
2x+3 = 0
x = -3/2

(4)
15x^2+31x+14=0
(3x+2)(5x+7)=0
3x+2 = 0 or 5x+7 = 0
x = -2/3 or x = -7/5

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