化简:sin^2(42°+α)-2tan(25°+α)tan(65°-α)+sin^2(48°-α)-cot^2(990°-α)

问题描述:

化简:sin^2(42°+α)-2tan(25°+α)tan(65°-α)+sin^2(48°-α)-cot^2(990°-α)