Решите неравенство: (√21 – 5)(5x – 1,5) > 0

х^(2)-0,5x-5<0

 x2 - 0.5x - 5 = 0
D = b2 - 4ac
D = 0.25 + 20 = 20.25 = (√20.25)^2

x1,2 = -b ± √D/2a
x1 = 0.5 + √20.25/2
x2 = 0.5 - √20.25/2
ответ: x1 = 0.5 + √20.25/2 ; x2 = 0.5 - √20.25/2

  x2 - 0.5x - 5 =a(x-x1)(x+x2)=(x-0.5 + √20.25/2)(x+0.5 - √20.25/2)

  (x-0.5 + √20.25/2)(x+0.5 - √20.25/2)<0 

21-5=16  а корень из 16 равно 4

4(5х-1.5)>0

20х-6>0

20x>6

x>20/6