已知x²-3x-1=0,求①x²+1/x²;②x²-1/x²

显示全部楼层 · 2013-1-5 21:27:52

x2-3x-1=0乘以x得x-3-1/x=0∴x-1/x=3x2+1/x2=(x-1/x)2+2=32+2=11(x+1/x)2=(x-1/x)2+4=32+4=13x+1/x=±√13x2-1/x2=(x+1/x)(x-1/x)=3×﹙±√13﹚=±3√13...

千问 · 2013-1-5 21:27:52

x2 - 3x - 1 = 0x - 1/x = 3 (x - 1/x)2 = 9x2 + 1/x2 = 11 (x + 1/x)2 = x2 + 1/x2 + 2 = 13 ①x2 + 1/x2 = 11 ②(x + 1...

千问 · 2013-1-5 21:27:52

已知x2-3x-1=0,x-3-1/x=0x-1/x=3x^2-2+1/x^2=9x^2+1/x^2=11x^2+2+1/x^2=11+2(x+1/x)^2=13x+1/x=±√13x2-1/x2=(x-1/x)(x+1/x)=±3√13...

千问 · 2013-1-5 21:27:52

x2-3x-1=0乘以x得x-3-1/x=0∴x-1/x=3x2+1/x2=(x-1/x)2+2=32+2=11(x+1/x)2=(x-1/x)2+4=32+4=13x+1/x=±√13x2-1/x2=(...