1/2－sin²67°30′
=1/2(1－2sin²67°30′)
=1/2cos(2×67°30′)
=1/2cos135°
=1/2[cos135°=cos(180°－45°)]
=1/2(cos180°cos45°＋sin180°sin45°)
=1/2(－1×√2/2＋0×√2/2
=1/2(－√2/2)
=－√2/4
=(1-2sin²67.5度)/2
=cos(2*67.5)/2
=cos135/2
=-√2/4
1/2-sin²67°30′
=1/2(1-2sin²67°30′)
=1/2cos135°
=-√2/4
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