问题标题：
y=2sin²B+sin(2B+π／6)=1+sin(2B-π／6)从前向后推,这是如何相等的啊,
问题描述：
y=2sin²B+sin(2B+π／6)=1+sin(2B-π／6)
从前向后推,这是如何相等的啊,
蔡朝洪回答：
cos(2B)=1-2sin²B
2sin²B=1-cos(2B)
y=2sin²B+sin(2B+π/6)
=1-cos(2B)+sin(2B)cos(π/6)+cos(2B)sin(π/6)
=1-cos(2B)+sin(2B)cos(π/6)+(1/2)cos(2B)
=1+sin(2B)cos(π/6)-(1/2)cos(2B)
=1+sin(2B)cos(π/6)-cos(2B)sin(π/6)
=1+sin(2B-π/6)
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