1) 0,255
2) -0,985
3) 3,(2) = 3,222
X+y=5
3x-2y=3
-----------
y=5-x
3x-2(5-x)=3
3x-10+2x=3, 5x=10+3, 5x=13, x=2,6
y=5-2,6=2,4,y=2,4
/x,y/=(2,6,,2,4/
1) 2х² <span>+ 5х - 7 = 0
D = 25 + 56 = 81
x</span>₁ =
<span>
x</span>₂ =
<span>
Два корня
2) 3х</span>² <span>- 7х - 8 = 0
</span>D = 49 + 96 = 145
<span>
x</span>₁ =
<span>
x</span>₂ =
<span>
Два корня
3) 4х</span>² <span>+ 4х + 1 = 0
D = 16 - 16 = 0
x</span>₁ =
<span>
Один корень
4) 9х</span>² - 6х + 2 = 0
D = 36 - 72 = -36
D < 0 (корней нет)
-2<a+1<7
a+1>-2
a>-3
a+1<7
a<6
Ответ: (-3: 6)