注意關系3π/8-θ=π/2-(π/8+θ)
5π/24-θ=π/2-(7π/24+θ)
所以原式=cos(3π/8-θ)cos(5π/24-θ)+cos(3π/8-θ)sin(7π/24+θ)
=cos(3π/8-θ)cos(5π/24-θ)+cos(3π/8-θ)cos(5π/24-θ)
=2cos(3π/8-θ)cos(5π/24-θ)
=cos(3π/8-θ-5π/24+θ)+cos(3π/8-θ+5π/24-θ)
=cosπ/6+cos(7/12π-2θ)
這是積化合差公式
cosA*cosB=1/2[cos(A-B)+cos(A+B)]
求值：cos(3π/8-θ)cos(5π/24-θ)+sin(π/8+θ)sin(7π/24+θ)
求值：cos(3π/8-θ)cos(5π/24-θ)+sin(π/8+θ)sin(7π/24+θ)
學到三角恒等式的 誘導公式 那里
求值：cos(3π/8-θ)cos(5π/24-θ)+sin(π/8+θ)sin(7π/24+θ)
我算到一半算不下去了
π是派(pai)哦...
=2cos(3π/8-θ)cos(5π/24-θ)
=cos(3π/8-θ-5π/24+θ)+cos(3π/8-θ+5π/24-θ)
只是搞不懂這兩步之間怎么變過去的...我自己就做到=2cos(3π/8-θ)cos(5π/24-θ) 這步
學到三角恒等式的 誘導公式 那里
求值：cos(3π/8-θ)cos(5π/24-θ)+sin(π/8+θ)sin(7π/24+θ)
我算到一半算不下去了
π是派(pai)哦...
=2cos(3π/8-θ)cos(5π/24-θ)
=cos(3π/8-θ-5π/24+θ)+cos(3π/8-θ+5π/24-θ)
只是搞不懂這兩步之間怎么變過去的...我自己就做到=2cos(3π/8-θ)cos(5π/24-θ) 這步
其他人氣：582 ℃時間：2020-06-18 16:59:09
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