a³b·﹙-4a³b﹚
=-4a^6b^2;
a²bⁿ·﹙-⅓aⁿb³﹚
=(-1/3)a^(n+2)b^(n+3);
-7/4a²bc·4/7ab²c·﹙-5ab﹚
=-a^3b^3c^2×(-5ab)
=5a^4b^4c^2;
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