\(4x^2-4x-y^2-8y-15\)
\(=\left(4x^2-4x+1\right)-\left(y^2+8y+16\right)\)
\(=\left(2x-1\right)^2-\left(y+4\right)^2\)
\(=\left(2x+y+3\right)\left(2x-y-5\right)\)
\(4x^2-4x-y^2-8y-15\)
\(=\left(4x^2-4x-1\right)-\left(y^2-8y-16\right)\)
\(=\left(4x^2-4x-1\right)-\left(y^2+8y+16\right)\)
\(=\left[\left(2x\right)^2-4x-1\right]-\left[y\left(y+8\right)\right]+16\)
\(=\left(2x^2-6x\right)\left(y+12\right)\left(y-4\right)\)
...