x3-5x2+5x-4
=(x³-4x²)-x²+5x-4
=x²(x-4)-(x-4)(x-1)
=(x-4)(x²-x+1)
x5+1/4x
=1/4x(4x4+1)
=1/4x(4x4+4x²+1-4x²)
=1/4x[(2x²+1)²-4x²]
=1/4x(2x²+2x+1)(2x²-2x+1)
9a4+11a2b2+4b4
=(9a4+12a2b2+4b4)-a²b²
=(3a²+2b²)-a²b²
=(3a²+ab+2b²)(3a²-ab+2b²)
（a2-5b2)2+(4ab)2
=a4-10a²b²+25b4+16a²b²
=a4+6a²b²+25b4
=a4+10a²b²+25b4-4a²b²
=(a²+5b²)²-4a²b²
=(a²+2ab+5b²)(a²-2ab+5b²)
a2-2a+4b-4b2
=(a+2b)(a-2b)-2(a-2b)
=(a-2b)(a+2b-2)