たとえば,
3x^4+2x^3+4x^2+2x+3=0
を解くためには,x≠0より,x^2で割って
3x^2+2x+4+2/x+3/x^2=0
3(x^2+1/x^2)+4+2(x+1/x)=0
X=x+1/xとおくと
3(X^2-2)+4+2X=0
3X^2+2X-2=0
X={-1±√7}/3
[1]x+1/x={-1+√7}/3
[2]x+1/x={-1-√7}/3
[1]3x^2+3={-1+√7}x
3x^2-{-1+√7}x+3=0
x={-1+√7}/6±i/6・√(28+2√7)
[2]3x^2+3={-1-√7}x
3x^2+{1+√7}x+3=0
x=-{1+√7}/6±i/6・√(28-2√7)
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