ta có : \(49\left(y-4\right)^2-9y^2-36y-36=49\left(y-4\right)^2-9\left(y^2+4y+4\right)\)
\(=\left(7\left(y-4\right)\right)^2-\left(3\left(y+2\right)\right)^2=\left(7\left(y-4\right)-3\left(y+2\right)\right)\left(7\left(y-4\right)+3\left(y+2\right)\right)\)
\(=\left(7y-28-3y-6\right)\left(7y-28+3y+6\right)=\left(4y-34\right)\left(10y-22\right)\)