a) \(1-2y+y^2=y^2-2y+1^2=\left(y-1\right)^2\)
b) \(\left(x+1\right)^2-25=\left(x+1\right)^2-5^2\)= \(\left(x+1+5\right).\left(x+1-5\right)=\left(x+6\right).\left(x-4\right)\)
c) \(1-4x^2=1^2-\left(2x\right)^2=\left(1+2x\right).\left(1-2x\right)\)
d) \(8-27x^3=2^3-\left(3x\right)^3=\left(2-3x\right).\left(4+6x+9x^2\right)\)