Solve by factorising

Solve by factorisation:

1. x² - 7x + 12 = 0
2. x² + x - 20 = 0
3. x² - 9 = 0
4. 2x² + 7x + 3 = 0
5. 3x² - 10x + 8 = 0
6. x² - 4x = 0

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