第1个回答 2013-12-01
cos(-225°-θ)+sin(435°+θ)=cos[-(225°+θ)]+sin[90*4+75+θ]=cos(180°-30°+75°+θ)+sin(75°+θ)
因为cos(75°+θ)=1/3,θ为第三象限角,所以sin(75°+θ)=-根号2/3.cos(180°-30°+75°+θ)=cos【180°-(30°-75°-θ)]=-cos(30°-75°-θ)=-cos[30°+(75°-θ)]=-【cos30°cos(75°-θ)-sin30°sin(75°-θ)】=-(根号3+根号2)/6,所以cos(-225°-θ)+sin(435°+θ)=-(根号3+根号2)/6-根号2/3=-(根号3+3根号2)/6