2) х²-0,7х-0,3<0<br>D= (-0.7)² -4*1*(-0.3) = 0.49+1.2=1.69=1.3²
x₁= (0.7-1.3)/(2*1) =- 0.6/2 = -0.3
x₂=(0.7+1.3)/2 = 2/2=1
Вычислим знаки на интервалах:
+ - +
------------o------------o------------
-0.3 1
-0,3x∈(-0.3 ; 1)
4) 12/49 - x+x² >0
x² -x + 12/49 >0
D= (-1)² - 4*1 * 12/49 = 1 - 48/49 = 1/49 = (1/7)²
x₁= (1- 1/7) / (2*1) = 6/7 : 2/1 = 6/7 * 1/2 = 3/7
x₂= (1 + 1/7) / 2 = 8/7 * 1/2 = 4/7
+ - +
----------o----------o-----------
3/7 4/7
3/7>x> 4/7
х ∈ (-∞ ; 3/7 ) ∪ ( 4/7 ; +∞)