РОЗДІЛ 4. Квадратні рівняння » 814 (6-8)

6) 3x² – 8x + 5 = 3(x – 5/3)(x – 1) = (3x – 5)(x – 1); D = (–8)2 – 4 • 3 • 5 = 64 – 60 = 4; x1 = (8-√4)/(2• 3) = (8-2)/6 = 6/6 = 1; x2 = (8+√4)/(2• 3) = (8+2)/6 = 10/6 = 5/3. 7) 4x² – 4x + 1 = (2x – 1)². 8) –2x² + 3x + 2 = –2(x + 1/2)(x – 2) = –(2x + 1)(x – 2); D = 32 – 4 • (–2) • 2 = 9 + 16 = 25. x1 = (-3-√25)/(2•(-2)) = (-3-5)/(-4) = (-8)/(-4) = 2; x2 = (-3+√25)/(2•(-2)) = (-3+5)/(-4) = 2/(-4) = –1/2.