wmjww
幼苗
共回答了19个问题采纳率:78.9% 举报
(1) x^2+y^2=(x-y)^2+2xy=10,所以,(y/x)+(x/y)=(x^2+y^2)/(xy)=10/3
(2)原式=[1/(x-1)- 1/(x+1)]- 2/(x²+1)- 4(x^4+1)- 8/(x^8+1)
=2/(x²-1)- 2/(x²+1)- 4(x^4+1)- 8/(x^8+1)
=4(x^4-1)- 4(x^4+1)- 8/(x^8+1)
=8/(x^8-1)- 8/(x^8+1)
=16/(x^16-1)
(3)原式=2/(x+4)+x/(x+4)
=(x+2)/(x+4)
带入x=3得 原式=5/7
上课要认真听啊,这可以锻炼思维
1年前
6