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sin²(a-π/6)+sin²(a+π/6)-sin²a
=(sinacosπ/6-sinπ/6cosa)²+(sinacosπ/6+sinπ/6cosa)²-sin²a
=(√3/2sina-1/2cosa)²+(√3/2sina+1/2cosa)²-sin²a
=3/4sin²a-√3/2sinacosa+1/4cos²a
+3/4sin²a+√3/2sinacosa+1/4cos²a-sin²a
=1/2sin²a+1/2cos²a
=1/2
1年前
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