Розділ 3. КВАДРАТНІ РІВНЯННЯ » 21.8 (4-6)

4) 1 – 4x = 5x2; 5x2 + 4x – 1 = 0; D = 42 – 4 • 5 • (–1) = 36; √D = 6; x1 = (-4+ 6)/(2 • 5 ) = 2/10 = 0,2; x2 = (-4- 6)/(2 • 5 ) = –1. 5) 81y2 + 1 = –18y; 81y2 + 18y + 1 = 0; D = 182 – 4 • 81 • 1 = 0; √D = 0; y = –18/(2 • 81 ) = –1/9. 6) 3p = 5p2 – 2; 5p2 – 3p – 2 = 0; D = (–3)2 – 4 • 5 • (–2) = 49; √D = 7; p1 = (3+ 7)/(2 • 5) = 1; p2 = (3- 7)/(2 • 5 ) = –0,4.