12x+15x-4x-5=8x-4x+10x-5 23x-5=14x-5 23x-14x=5-5 9x=0 x=0
(3x-1)(4x+5)=(4x+5)(2x-1) 12x+15x-4x-5=8x-4x+10x-5 12x+15x-4x-8x+4x-10x=-5+5 9x=0/:9 x=0