\(25\left(x-3\right)^2-\left(2x-7\right)^2\)(*)
Đặt \(x-3=t\)và \(2x-7=z\)thay vào (*) ta được:
\(25t^2-z^2\)
\(=\left(5t-z\right)\left(5t+z\right)\)thay t=x-3 và y=2x-7 ta được:
\(=\left(5x-15-2x+7\right)\left(5x-15+2x-7\right)\)
\(=\left(3x-8\right)\left(7x-22\right)\)
C2 nhân ra rồi phân tích
\(25\left(x-3\right)^2-\left(2x-7\right)^2\)
\(=5^2.\left(x-3\right)^2-\left(2x-7\right)^2\)
\(=\left[5.\left(x-3\right)\right]^2-\left(2x-7\right)^2\)
\(=\left[5\left(x-3\right)-\left(2x-7\right)\right]\left[5\left(x-3\right)+\left(2x-7\right)\right]\)
\(=\left(5x-15-2x+7\right)\left(5x-15+2x-7\right)\)
\(=\left(3x-8\right)\left(7x-22\right)\)
