1) х² - х -56 = 0
D = b² - 4ac = (-1)² - 4 ×1 × (-56) = 225
1 - √225 1 - 15 - 14
Х1 = ----------------- = ------------------- = ---------- = - 7
2 * 1 2 2
1 + √225 1 + 15 16
Х2 = --------------------- = --------------- = ----------- = 8
2 * 1 2 2
2) S = a² * sin 30 = 8² * 1/2 = 64 * 1/2 = 32
3) 500 * 2 : 100 = 10
500 - 10 = 490 было перечислено