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1.求方程式的根0=x^4+x^2+1
=(y-1)(y^2+y+1).....y=x^2
=y^3-1
y^3=1=cos360°+jsin360°
y=(cos360°+jsin360°)^(1/3)
y1=cos120°+jsin120°.....戴美弗定理
y2=cos240°+jsin240°
y3=cos360°+jsin360°
x1=+-(cos120°+jsin120°)^0.5
=+-(cos60°+jsin60°)
=+-(1+j√3)/2
x2=+-(cos240°+jsin240°)^0.5
=+-(cos120°+jsin120°)
=+-(-1+j√3)/2
2.求x^5+x^4+x^3+x^2+x+1=0所圍成五邊形之面積
0=x^6-1=(x-1)(x^5+x^4+x^3+x^2+x+1)
x^6=1=cos360°+jsin360°
x=(cos360°+jsin360°)^(1/6)
x1=cos60°+jsin60°.....戴美弗定理
x2=cos120°+jsin120°
x3=cos180°+jsin180°
x4=cos240°+jsin240°
x5=cos300°+jsin300°
此5邊形: 每兩者夾角=60°,每邊長=1
只有x1,x5的夾角=120°
所以面積為:
A=4pc*0.5*1*1*sin60°+0.5*1*1*sin120°
=2*√3/2+0.5*√3/2
=√3+√3/4
=5√3/4.....ans
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