а)x² - 7x - 9 = 0
D = b² - 4ac = (-7)² - 4·1·(-9) = 49 + 36 = 85
x₁ = (7 - √85)/2
x₂ = (7 + √85)/2
б)2x² + 8x - 19 = 0
D = b² - 4ac = 8² - 4·2·(-19) = 64 + 152 = 216
x₁ = (-8 - √216)/(2·2) = -2 - 1.5√6
x₂ = (-8 + √216)/(2·2) = -2 + 1.5√6
в)5x² - 7x = 0
D = b² - 4ac = (-7)² - 4·5·0 = 49 - 0 = 49
x₁ = (7 - √49)/(2·5) = (7 - 7)/10 = 0/10 = 0
x₂ = (7 + √49)/(2·5) = (7 + 7)/10 = 14/10 = 1.4
г) 13x² - 25 = 0
D = b² - 4ac = - 4·13·(-25) = 1300 = 1300
x₁ = - √1300/(2·13) = -(5√13)/13
x₂ = √1300/(2·13) = (5√13/) /13