■代数学の基本定理とiの1/2乗とガロア理論(その3)
iのi乗について
iのiのi乗について扱ってきたが、ここでは
i=cos(π/2+2nπ)+isin(π/2+2nπ)
i^1/3=cos(π/6+2nπ/3)+isin(π/6+2nπ/3)
n=0のとき
i^1/3=cos(π/6)+isin(π/6)=1/2(√3+i)
n=1のとき
i^1/3=cos(5π/6)+isin(5π/6)=1/2(-√3+i)
n=2のとき
i^1/3=cos(3π/2)+isin(3π/2)=-i
===================================
±1の3乗方根も求めてみたい。
1=cos(2nπ)+isin(2nπ)
-1=cos(π+2nπ)+isin(π+2nπ)
1^1/3=cos(2nπ/3)+isin(2nπ/3)
(-1)^1/3=cos(π/3+2nπ/3)+isin(π/3+2nπ/3)
n=0のとき
1^1/3=cos(0)+isin(0)=1
(-1)^1/3=cos(π/3)+isin(π/3)=1/2(1+√3i)
n=1のとき
1^1/3=cos(2π/3)+isin(2π/3)=1/2(-1+√3i)=ω
(-1)^1/3=cos(π)+isin(π)=-1
n=2のとき
1^1/3=cos(4π/3)+isin(4π/3)=1/2(-1-√3i)=ω^2
(-1)^1/3=cos(5π/3)+isin(5π/3)=1/2(1-√3i)
===================================