m²/9+1-2m/3
=(m/3)²-2m/3+1
=(m/3-1)²
4-12(x-y)+9(x-y)²
=[3(x-y)]²-12(x-y)+2²
=(3x-3y-2)²
x^4-2x²+1
=(x²)-2x²+1
=(x²-1)²
=(x-1)(x+1)(x-1)(x+1)
=(x-1)²(x+1)²