form2既主項變換.

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http://img14.imageshack.us/img14/51/screenhunter01nov172342.gif

已知x=1/n+1及y=n/n-1.
a(1)
試以x表示n.
x = 1/(n+1)
x(n+1) = 1
xn+x=1
xn = 1-x
n = (1-x)/x
(2)
試以y表示n.
y = n/(n-1)
y(n-1) = n
yn-y = n
yn-n = y
n(y-1) = y
n = y/(y-1)

b(1)
試以x表示y.
當a(1)=a(2)
(1-x)/x = y/(y-1)
(1-x)(y-1) = xy
y-1-xy+x=xy
y-xy-xy = 1-x
y-2xy = 1-x
y(1-2x) = 1-x
y = (1-x)/(1-2x)
y = [-(x-1)]/[-(2x-1)]
y = (x-1)/(2x-1)

(2)
試以y表示x.
由b(1),
y-1-xy+x=xy
x-xy-xy = 1+y
x-2xy = 1+y
x(1-2y) = 1+y
x = (1+y)/(1-2y)
x = [-(y-1)]/[-(2y-1)]
x = (y-1)/(2y-1)