sinx + sin3x = 2sin2xcosx
係邊條公式變出來的?
A.maths:sine cosine
2007-04-13 5:46 am
回答 (2)
2007-04-13 6:29 am
✔ 最佳答案
左面係相加 , 右面係相乘所以會由"和差化積公式" (sum-to-product)變出來
sin x + sin 3x = 2 sin [(x+3x)/2] cos [(x-3x)/2]
= 2 sin 2x cos (-x)
= 2 sin 2x cos x ＜＝[cos (-x) = cos x]
參考: by My Maths
2007-04-13 6:01 am
LHS=RHS
LHS = sinx+sin3x
= 2sin2xcosx <--(sinx+siny=2sin((x+y)/2)cos((x-y)/2)) {Sum to Product}
LHS = sinx+sin3x
= 2sin2xcosx <--(sinx+siny=2sin((x+y)/2)cos((x-y)/2)) {Sum to Product}
收錄日期: 2021-04-13 00:42:47
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