①x⑤+②x⑥

((6n^3+20n^2-n-27)(n-1)/24)(((-1)^(n+1)+1)/2)+((6n^4+14n^3-21n^2-26n+24)/24)(((-1)^n+1)/2)

∴P1st =｛12n^4+28n^3-42n^2-52n-3(-1)^n+51｝/48

③x⑤+④x⑥

((6n^2+10n-3)(n+1)(n-1)/24)(((-1)^(n+1)+1)/2)+((6n^2-2n-5)(n+2)n/24)(((-1)^n+1)/2)

∴Q1st =｛12n^4+20n^3-18n^2-20n-3(-1)^n+3｝/48

>>7と一致Match