\(x^2-2xy-4z^2+y^2\)
\(=\left(x^2-2xy+y^2\right)-4z^2\)
\(=\left(x-y\right)^2-\left(2z\right)^2\)
\(=\left(x-y-2z\right)\left(x-y+2z\right)\)
Thay ............... :
\(\left(\left(-4\right)-y-2.45\right)\left(\left(-4\right)-y+2.45\right)\)
\(=\left(-y-49\right)\left(86-y\right)\)