来自胡麒的问题
1.已知xy=1,x=2+√3,求1/(x+1)+1/(y-1)的值2.已知x=2+√3,y=2-√3,求x3+x2y+xy2+y3的值(字母后的数字为次方)
1.已知xy=1,x=2+√3,求1/(x+1)+1/(y-1)的值
2.已知x=2+√3,y=2-√3,求x3+x2y+xy2+y3的值(字母后的数字为次方)
1回答
2019-07-14 12:23
1.已知xy=1,x=2+√3,求1/(x+1)+1/(y-1)的值2.已知x=2+√3,y=2-√3,求x3+x2y+xy2+y3的值(字母后的数字为次方)
1.已知xy=1,x=2+√3,求1/(x+1)+1/(y-1)的值
2.已知x=2+√3,y=2-√3,求x3+x2y+xy2+y3的值(字母后的数字为次方)
1、因为xy=1,x=2+√3,可得y=1/(2+√3)=(2-√3)/[(2+√3)(2-√3)]=2-√3
所以1/(x+1)+1/(y-1)
=[(y-1)+(x+1)]/[(y-1)(x+1)]
=(x+y)/(xy+y-x-1)
将x、y的值代入上式得:
(x+y)/(xy+y-x-1)
=4/[(2+√3)*(2-√3)+2-√3-2-√3-1]
=4/(3-2√3)
=[4*(3+2√3)]/[(3-2√3)*(3+2√3)]
=(-3-2√3)/3
2、由已知可得x+y=4,xy=1
x3+x2y+xy2+y3
=(x+y)^3-3x^2y-3xy^2+x^2y+xy^2
=(x+y)^3-2xy(x+y)
将x+y和xy的值代入上式得:
(x+y)^3-2xy(x+y)
=4^3-2*4*1
=64-8
=56