kevin2437
幼苗
共回答了19个问题采纳率：100% 举报
2sina(sina+cosa)-1
=2sina^2-1+2sinacosa
=-cos(2a)+sin(2a) [sin2a=2sinacosa cos2a=1-2sina^2]
=√2[sin2acosπ/4-cos2asinπ/4] 三角公式
=√2sin(2a-π/4)
sin(a-π/8)=3/5 则
cos（a-π/8）=-4/5 由于5π/8
sin(2a-π/4)=2sin(a-π/8)*cos（a-π/8）=2*（3/5）*（-4/5）=-24/25
则原始=√2sin(2a-π/4)=-24√2/25
1年前
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