急!已知cos(75°+θ)=1/3.θ为第三象限角求值:cos(-255°-θ)+sin(435°+θ)
问题描述:
急!已知cos(75°+θ)=1/3.θ为第三象限角求值:cos(-255°-θ)+sin(435°+θ)
答
cos(-180-75-θ)+sin(360+75+θ)=-cos(75+θ)+sin(75+θ)=-1/3-2√2/3=-(1+2√2)/3