✨ Best Answer ✨
加法定理を用います
【cos(α－β)＝cosα･cosβ＋sinα･sinβ】
cos{(π/12)}
＝cos{(π/4)－(π/6)}
＝cos(π/4)･cos(π/6)＋sin(π/4)･sin(π/6)
＝(1/√2)･(√3/2)＋(1/√2)･(1/2)
＝(√6＋√2)/4
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