x+y=(√7+√5+√7-√5)/2=√7xy=(√7+√5)(√7-√5)/4=(7-5)/4=1/2(x+y)²=(√7)²x²+y²+2xy=7x²+y²=7-2xy=6所以x²-xy+y²=6-1/2=11/2y/x+x/y=(x²+y²)/xy=12
