Неравенства

1) 4-2x<9

2) x^2-4x-21>0

3) 1-16x^2>0

4) 7x-21x^2<0

1) 4-2x - 2x x>2.5

2) x^2-4x-21>0 = > D = (-4) ^2-4 * (-21) = 16+84=100=10; x1 = (4+10) / 2=7; x2 = (4-10) / 2=-3; Ответ: (-3; 7)

3) 1-16x^2>0 = > - 16x^2>-1 = > 4x x< 0.25

4) 7x-21x^2 7-21x - 21x x<1/3