若θ是第三象限角,且满足cosθ /2-sinθ /2=|sinθ/2-cosθ/2|,则θ/2是第几象限角?
问题描述：
若θ是第三象限角,且满足cosθ /2-sinθ /2=|sinθ/2-cosθ/2|,则θ/2是第几象限角?
答
cosθ /2-sinθ /2=|sinθ/2-cosθ/2|所以cosθ /2-sinθ /2＜0（1/√2）sin(π/4-θ)＜0sin(θ-π/4)＞02πn＜θ-π/4＜π+2πnπ/4+2πn＜θ＜5π/4+2πnθ又在第三象限所以π+2πn＜θ＜5π/4+2πnπ/2+πn＜θ/2...