Question

phân tích đa thức sau thành nhân tử

c) \(49\left(y-4\right)^2-9y^2-36y-36\)

Answer 1

    

      \(49\left(y-4\right)^2-9y^2-36y-36\)

\(=\left[7\left(y-4\right)\right]^2-\left[\left(3y\right)^2+2.3y.6+6^2\right]\)

\(=\left(7y-28\right)^2-\left(3y+6\right)^2\)

\(=\left(7y-28-3y-6\right)\left(7y-28+3y+6\right)=\left(4y-34\right)\left(10y-22\right)=4\left(2y-17\right)\left(5y-11\right)\)

Answer 2

\(49\left(y-4\right)^2-9y^2-36y-36=49\left(y-4\right)^2-9\left(y^2+4y+4\right)\)\(=\left[7\left(y-4\right)\right]^2-\left[3\left(y+4\right)\right]^2=\left(7y-28-3y-12\right)\left(7y-28+3y+12\right)\)\(=\left(4y-40\right)\left(10y-16\right)=4\left(y-20\right)\left(5y-8\right)\)