(2*4*6.*2n)/(1*3*5.*(2n-1))=?
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(2*4*6.*2n)/(1*3*5.*(2n-1))=?
分子分母同乘以分子,如下:
(2*4*6.*2n)/(1*3*5.*(2n-1))
=(2*4*6.*2n)^2/(2n)!
=2^(2n)*(n!)^2/(2n)!
(2*4*6.*2n)/(1*3*5.*(2n-1))
=(2*4*6.*2n)^2/(2n)!
=2^(2n)*(n!)^2/(2n)!
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