\(b,x^2-4x-9y^2+4=\left(x-2\right)^2-\left(3y\right)^2=\left(x-2-3y\right)\left(x-2+3y\right)\)
\(c,x^2-2x-4x^2+1=\left(x-1\right)^2-\left(2x\right)^2=\left(x-1+2x\right)\left(x-2x-1\right)=\left(3x-1\right)\left(-x-1\right)\)
\(d,4x^2-6x-9y^2+9y=\left(4x^2-9y^2\right)-\left(6x-9y\right)=\left(2x-3y\right)\left(2x+3y\right)-3\left(2x-3y\right)=\left(2x+3y-3\right)\left(2x-3y\right)\)