РОЗДІЛ 4. Квадратні рівняння » 812 (3-4)

3) –x² + 16x – 15 = –(x – 15)(x – 1); D = 162 – 4 • (–1) • (–15) = 256 + 60 = 196. x1 = (-16-√196)/(2•(-1)) = (-16-14)/(-2) = (-30)/(-2) = 15; x2 = (-16+√196)/(2•(-1)) = (-16+14)/(-2) = (-2)/(-2) = 1. 4) x² – 2x – 15 = (x + 3)(x – 5); D = (–2)2 – 4 • 1 • (–15) = 4 + 60 = 64. x1 = (2-√64)/(2•1) = (2-7)/2 = (-6)/2 = –3; x2 = (2+√64)/(2•1) = (2+8)/(2•1) = 10/2 = 5.