赞 chendali 幼苗
共回答了16个问题采纳率：81.3% 举报
cos2a/sin(a-π/4)=(2cos2a*cos(a-π/4)) /(2sin(a-π/4) cos(a-π/4))
cos2a/sin(a-π/4)=(2cos2a*cos(a-π/4)) /sin(2a-π/2)
cos2a/sin(a-π/4)=-(2cos2a*cos(a-π/4)) /cos2a
cos2a/sin(a-π/4)=-2*cos(a-π/4)
-2*cos(a-π/4) =-√2/2
cos(a-π/4) =√2/4
cosa*cos(π/4)+sina*sin(π/4)=√2/4
cosa+cosb=1/2
cos2a/sin(a-π/4)=(2cos2a*cos(a-π/4)) /sin(2a-π/2)
cos2a/sin(a-π/4)=-(2cos2a*cos(a-π/4)) /cos2a
cos2a/sin(a-π/4)=-2*cos(a-π/4)
-2*cos(a-π/4) =-√2/2
cos(a-π/4) =√2/4
cosa*cos(π/4)+sina*sin(π/4)=√2/4
cosa+cosb=1/2
1年前
3
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你能帮帮他们吗