2cos^2(67°30′)=

问题描述:

2cos^2(67°30′)=

2cos^2(67°30′)=1+cos135°=1-√2/2噢,谢谢你!可不可以再帮我看看这一题? sin^4(112°30′)-cos^4(112°30′) =sin^4(112°30′)-cos^4(112°30′)=[sin^2(112°30′)-cos^2(112°30′)][sin^2(112°30′)+cos^2(112°30′)]=sin^2(112°30′)-cos^2(112°30′)=-cos(112°30′*2)=-cos(225°)=cos(135°)=-√2/2