Ta có: \(5\left(3x^{n+1}-y^{n-1}\right)-3\left(x^{n+1}+2y^{n-1}\right)+4\left(-x^{n+1}+2y^{n-1}\right)\)
\(=15x^{n+1}-5y^{n-1}-3x^{n+1}-2y^{n-1}-4x^{n+1}+8y^{n-1}\)
\(=\left(15x^{n+1}-3x^{n+1}-4x^{n+1}\right)-\left(5y^{n-1}+2y^{n-1}-8y^{n-1}\right)\)
\(=8x^{n+1}+y^{n-1}\)