12. 5x² - 180 = 0
5x² = 0 + 180
5x² = 180
x² = 180/5
x² = 36
x = √36
x = 6
13. 3x² - 100 = 332
3x² = 332 + 100
3x² = 432
x² = 432/3
x² = 144
x = √144
x = 12
14. ⅔x² - 8 = 16
⅔x² = 16 + 8
⅔x² = 24
2x² = 24 × 3
2x² = 72
x² = 72/2
15. ½x² - 5 = 5
½x² = 5 + 5
½x² = 10
x² = 10 × 2
x² = 20
x = √20
16. x² + 1 = 3x² - 13
1 + 13 = 3x² - x²
14 = 2x²
14/2 = x²
7 = x²
√7 = x
17. 2(x² + 4) = 10
2x² + 8 = 10
2x² = 10 - 8
2x² = 2
x² = 2/2
x² = 1
x = √1
x = 1
18. 3(x² - 1) = 9
3x² - 3 = 9
3x² = 9 + 3
3x² = 12
x² = 12/3
x² = 4
x = √4
x = 2
19. 2(x + 3)² = 8
2(x² + 3² + 2×x×3) = 8
2(x² + 9 + 6x) = 8
2x² + 18 + 12x = 8
2x² + 12x = 8 - 18
2x² + 12x = -10
2(x² + 6x) = -10
x² + 6x = -10/2
x(x + 6) = -5
x + 6 = -5/x
6 = -5/x - x
6 = -5/x - x²/x
6 = (-5 -x²)/x
6x = -5 - x²
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