设x1,x2是方程3x方-5x-7=0的两根.求(1)x1方+x2方=?(2)1/x1+1/x2=?(3)X2/X1+X1/X2=?

问题描述:

设x1,x2是方程3x方-5x-7=0的两根.求(1)x1方+x2方=?(2)1/x1+1/x2=?(3)X2/X1+X1/X2=?

x"表示x的平方3x"-5x-7=0∴x1+x2 = 5/3,x1*x2 = -7/3x1"+x2" = (x1+x2)" -2x1x2 = 25/9 +14/3 = 67/91/x1+1/x2 = (x1+x2)/x1x2 = -5/7x2/x1+x1/x2 = x1"+x2"/x1x2 = -67/21