>>658
左辺
=4*n(n-1)(n-2)(n-3)/1*2*3*4÷4n(4n-1)(4n-2)(4n-3)
=4n(n-1)(n-2)(n-3)/4n(4n-1)(4n-2)(4n-3)
=(n-1)(n-2)(n-3)/(4n-1)(4n-2)(4n-3)