试说明：无论x、y取何值,代数式（x³+3x²y-5xy²+6y³）+(y³+2xy²+x²y-2x³-2)-(4x²y-x³-3xy²+7y³-5)的值是常数.

试说明：无论x、y取何值,代数式（x³+3x²y-5xy²+6y³）+(y³+2xy²+x²y-2x³-2)-(4x²y-x³-3xy²+7y³-5)的值是常数.
试说明：无论x、y取何值,代数式（x³+3x²y-5xy²+6y³）+
(y³+2xy²+x²y-2x³-2)-(4x²y-x³-3xy²+7y³-5)的值是常数.

试说明：无论x、y取何值,代数式（x³+3x²y-5xy²+6y³）+(y³+2xy²+x²y-2x³-2)-(4x²y-x³-3xy²+7y³-5)的值是常数.
(x³+3x²y-5xy²+6y³)+(y³+2xy²+x²y-2x³-2)-(4x²y-x³-3xy²+7y³-5)
=x³+3x²y-5xy²+6y³+y³+2xy²+x²y-2x³-2-4x²y+x³+3xy²-7y³+5
=3