a)
(x-1)²(x+5)²(x-2)²=0
[(x-1)(x+5)(x-2)]²=0
x-1=0 ∨ x+5=0 ∨ x-2=0
x=1 ∨ x=-5 ∨ x=2
x∈{-5,1,2}
b)
8x(2-x)²(x²+6x-7)=0|:8
x(2-x)²(x²+6x-7)=0
x=0 ∨ 2-x=0 ∨ x²+6x-7=0
x=0 ∨ x=2 Δ=6²-4·1·(-7)=36+28=64 , √Δ=√64=8
x1=(-6-8)/2 ∨ x2=(-6+8)/2
x1=-7 ∨ x2=1
x∈{-7,0,1,2}