回复：有没有好办法？

note each sides lengths as:
x+y=130,
x+b=90
b+a=70
a+y=110. This group of equations are from the inner circle. However the last one is redundent.

Then connect the inner circle's center with the vertices, use the condition of the outer circle, you get this equation; xa=yb. (due to the fact that the opposite angles are compliment to each other).

Solve the equations you get y-x=13.

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• 回复：回复：有没有好办法？ -cma- ♂ (14 bytes) () 03/09/2009 postreply 08:40:19