Verified answer

ax² + bx + c = 0

D = b² - 4ac

x12 = (-b +- √D)/2a

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x² + 7x - 60 = 0

D = b² - 4ac = 49 + 240 = 289

x12 = (-7+-17)/2 = 5 и  - 12

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m² + m - 90=0

D = 1 + 360 = 361

m12=(-1 +- 19)/2 = -10 и 9

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3x² + 32x + 80 = 0

D = 32² - 4*3*80 = 1024 - 960 = 64

x12 = (-32 +- 8)/6 = -4 и -20/3

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3x² - 6x + 3 = 0

x² - 2x + 1 =0

(x-1)² = 0

x = 1