(1-16a^4)/(4a^2+1)/(2a+1)
=(1+4a^2)(1-4a^2)/[(4a^2+1)(2a+1)]
=(1+4a^2)(1+2a)(1-2a)/[(4a^2+1)(2a+1)]
=1-2a
(2cxy^2-4cx^2y)/(y-2x)
=2cxy(y-2x)/(y-2x)
=2cxy
[4x^2-(y-3x)^2]/(x-y)
=(2x+y-3x)(2x-y+3x)/(x-y)
=(y-x)(5x-y)/(x-y)
=-(x-y)(5x-y)/(x-y)
=-(5x-y)
=y-5x