7777×8888-5555×4444
=(7×8-5×4)×1111×1111
=36×1111×1111
=36×(1000+111)^2
=36×(1000^2+2×111×1000+111^2)
=36×(1000000+222000+(100+11)^2)
=36×(1222000+100^2+2×11×100+11^2)
=36×(1222000+10000+2200+121)
=36×1234321
=44435556