1) 21x^2 + 39x - 6 < 0
x < 0
21x^2 + 39x - 6 = 0
D = 39^2 + 4*21*6 = 2025
x1 = (-39 + 45)/12 = 6/12 = 1/2
x2 = (-39 - 45)/12 = -84/12 = -7
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Ответ х E(-7; 0)
2) 4x^2 + 5x - 6 > 0
x > 0
4x^2 + 5x - 6 = 0
D = 25 + 4*4*6 = 121
x1 = (-5 + 11)/8 = 6/8 = 3/4
x2 = (-5 - 11)/8 = -16/8 = -2
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ответ x E (3/4; + беск.)