请教几道数学题目~~谢谢

1,x+y=(x^2-y^2)/(x-y)=11

2.(n+2)^2=n^2+4(n+1)

3.(1+1/2)*(1+1/2^2(二的二次方分之一)*(1+1/2^4)*(1+1/2^8)*1/2^15
=(1-1/2)*(1+1/2)*(1+1/2^2(二的二次方分之一)*(1+1/2^4)*(1+1/2^8)*1/2^15*1/(1-1/2)
=(1-1/2^16)/[2^15*(1-1/2)]
=(1-1/2^16)/2^16
=1/2^16-1/2^32

100^2-99^2+98^2-97^2……+2^2-1
=(100+99)(100-99)+(98+97)(98-97)+...+(2+1)(2-1)
=199+195+191+...+3
=(3+199)*50/2
=5050

4.x^2-3x+1=0,X=0不是它的解，所以X不=0，
等式两边都除以X，得
x-3+1/x=0
x+1/x=3

2)x^2+1/x^2=(x+1/x)^2-2x*1/x
=(x+1/x)^2-2=9-2=7

1、计算100^2-99^2+98^2-97^2+96^2-95^2+……2^2-1^2=________
=(100+99)*(100-99)+(98+97)*(98-97)+(96+95)*(96-95)+...+(2+1)(2-1)
=199+195+191+...+3
=(199+3)*50/2
=5050

1.X^2-Y^2=(X+Y)(X-Y)=(X+Y)*5=55
so:X+Y=11