2.
a)
x²-14x+40≥0
x²-14x+40=0
D=(-14)² -4*40=196-160=36=6²
x₁=(14-6)/2=8/2=4
x₂=(14+6)/2=20/2=10
+ - +
--------- 4 ------------ 10 ---------------
\\\\\\\\\\ \\\\\\\\\\\\\\
x∈(-∞; 4]U[10; +∞)
D(y)=(-∞; 4]U[10; +∞)
б)
8x-2x²>0
-2x(x-4)>0
x(x-4)<0<br>x=0 x=4
+ - +
--------- 0 ----------- 4 ------------
\\\\\\\\\\\\
x∈(0; 4)
D(y)=(0; 4).
3)
(2+7x)² ≤(4-3x)²
(2+7x)² - (4-3x)² ≤0
(2+7x-4+3x)(2+7x+4-3x)≤0
(10x-2)(4x+6)≤0
10(x-0.2)*4(x+1.5)≤0
(x-0.2)(x+1.5)≤0
x=0.2 x= -1.5
+ - +
---------- -1.5 ------------- 0.2 -----------
\\\\\\\\\\\\\\\\
x∈[-1.5; 0.2]
Ответ: [-1.5; 0.2].