a) (x-1)²-25=(x-1-5)(x-1+5)=(x-6)(x+4)=0, x₁=6, x₂=-4 b)(x-2)²-(2x-1)²=(x-2-2x+1)(x-2+2x-1)=(-x-1)(3x-3)=0, x₁=-1, x₂=1