\(=\left(18x^{2n-3}+3x^n\right)-\left(18x^{2n-3}-2x^n\right)\)
\(=18x^{2n-3}+3x^n-18x^{2n-3}+2x^n\)
\(=\left(18x^{2n-3}-18x^{2n-3}\right)+\left(3x^n+2x^n\right)\)
\(=5x^n\)

\(=18x^{2n-3}+3x^n-18x^{2n-3}+2x^n=5x^n\)

\(3x^n.\left(6x^{n-3}+1\right)-2x^n.\left(9x^{n-3}-1\right)\)

\(=18x^{n+n-3}+3x^n-18x^{n+n-3}+2x^n\)

\(=18x^{2n-3}+3x^n-18^{2n-3}+2x^n\)

\(=3x^n+2x^n=x^n\left(3+2\right)=5x^n\)

a: 

=\(18x^{2n-3}+3x^n-18^{2n-3}+2x^n\)

\(=5x^n\)

b: \(=5^n\cdot5-4\cdot5^n=5^n\)

c: \(=6^6-4^3\cdot3^6+4^3\)

\(=2^6\cdot3^6-2^6\cdot3^6+64=64\)

a) Ta có: \(x^{n-1}\left(x+y\right)-y\left(x^{n-1}+y^{n-1}\right)\)

\(=x^n+x^{n-1}\cdot y-x^{n-1}\cdot y-y\cdot y^{n-1}\)

\(=x^n-y^n\)

a) \(x^{n-1}\left(x+y\right)-y\left(x^{n-1}+y^{n-1}\right)\)

\(=x^{n-1}x+x^{n-1}y-x^{n-1}y-y^{n-1}y\)

\(=x^n-y^n\)

b) \(6x^n\left(x^2-1\right)+2x^3\left(3x^{n+1}+1\right)\)

\(=6x^nx^2-6x^n+2x^33x^{n+1}+2x^3\)

\(=6x^{n+2}-6x^n+6x^{3+n+1}+2x^3\)

\(=6x^{n+2}-6x^n+6x^{n+4}+2x^3\)

Đề có sai ko vậy bạn ???

\(3x^n\left(6x^{n-3}+1\right)-2x^n\left(9x^{n-3}-1\right)\)

\(=3x^n\cdot6x^{n-3}+3x^n-2x^n\cdot9x^{n-3}+2x^n\)

\(=18x^{2n-3}+3x^n-18^{2x-3}+2x^n\)

\(=3x^n+2x^n\)

\(=5x^n\)

\(=18x^{2n-3}+3x^n-18x^{2n-3}+2x^n=5x^n\)

\(3x^n\left(6x^{n-3}+1\right)-2x^n\left(9x^{n-3}-1\right)\)

\(=18x^{2n-3}+3x^n-18x^{2n-3}+2x^n\)

\(=3x^n+2x^n\)

\(=5x^n\)