假设n=k(k>=r)时,等式成立,即rCr+(r+1)Cr+.+kCr=(k+1)C(r+1),那么n=k+1时有rCr+(r+1)Cr+.+kCr+(k+1)Cr=(k+1)C(r+1)+(k+1)Cr=(k+2)C(r+1),即n=k+1时等式也成立.综上,对n>=r的自然数n,rCr+(r+1)Cr+.+nCr=(n+1)C(r+1)均成立....
1Mn18Cr18N钢护环裂纹性质和材质状态分析
T h e corlccntration of alllumin iri tllc pooled sera was 3.6 g/cll a s detcrrnincd by the brorncrcsol grccn mctliod ( 7 ) . Stand;~rdt>iliruhin solutions \\.ere m;ltlc from a I'reslily prcl>;ircd solution of 7 0 0 nlg/dl of cryst:~llincbilirubin ( I S ) clissol...
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