-(x-2)(9-x)(x+10)>0
(x-2)(x-9)(x+10)>0
x=2 x=9 x= -10
- + - +
--------- -10 ---------- 2 ------------- 9 -----------
\\\\\\\\\\\\\ \\\\\\\\\\\\\\
(-∞; -10) x= -11 - - - | -
(-10; 2) x=0 - - + | +
(2; 9) x=3 + - + | -
(9; +∞) x=10 + + + | +
x∈(-10; 2)U(9; +∞)
Cos7x - cosx = 0
- 2sin(7x + x)/2 * sin(7x - x)/2 = 0
sin4x * sin3x = 0
1) sin4x = 0
4x = πk, k∈Z
x₁ = πk/4, k∈z
2) sin3x = 0
3x = πn, n∈Z
x₂ = πn/3, n∈Z
А5=2+(5*4)=22
s5=2+7+12+17+22=60