解:已知?$4×16^{m}×64^{m}=4^{21}$?
∵?$4 = 2^2,$??$16 = 2^4,$??$64 = 2^6$?
∴?$2^2×2^{4m}×2^{6m}=2^{2 + 4m + 6m}=2^{2+10m},$?又?$4^{21}=(2^2)^{21}=2^{42}$?
?$ $?則?$2 + 10m = 42,$?解得?$m = 4$?
原式?$=(-1)^3·(\mathrm {m^2})^3÷m^{3 + 2}=-m^6÷ m^5=-m$?
?$ $?把?$m = 4$?代入可得?$-m=-4$?