610
8x-4+3-6x=7
8x-6x=7+4-3
2x=8
x=4
4x+8-6x+4=14x-5x-15
4x-6x-9x=4-15-8
-11x=-19
x=19/11
10 Cos² x + 3 Cos x -1 = 0
t = Cos x, |t| ≤ 1
10t² +3t -1 = 0
D = 9 +40 = 49
t = (-3 -7)/20 = -1/2
t = (-3+7)/20 = 1/5
Cos x = -1/2
x = ± 2π/3 +2πn, n ∈ Z
Cos x = 1/5
x = ± arccos(1/5) +2πn, n ∈ Z