Розділ 3. КВАДРАТНІ РІВНЯННЯ » 21.8 (1-3)

Розв’яжіть рівняння: 1) 10x2 = 5x + 0,6; 10x2 – 5x – 0,6 = 0; D = (–5)2 – 4 • 10 • (–0,6) = 25 + 24 = 49; √D = 7; x1 = (5+ 7)/(2 •10) = 12/20 = 0,6; x2 = (5- 7)/(2 • 10) = –2/20 = –0,1. 2) x2 + 3 = 4x; x2 – 4x + 3 = 0; D = (–4)2 – 4 • 1 • 3 = 4; √D = 2; x1 = (4+ 2)/(2 ) = 3; x2 = (4- 2)/(2 ) = 1. 3) x2 + 5x = –6; x2 + 5x + 6 = 0; D = 52 – 4 • 1 • 6 = 1; √D = 1; x1 = (-5+ 1)/(2 ) = (-4)/2 = –2; x2 = (-5- 1)/(2 ) = –3.