r=1∑3030Cr−1r2(30Cr)2=r=1∑30r2(r31−r)⋅r!(30−r)!30!(∵30Cr−130Cr=r30−r+1=r31−r) =r=1∑30(r−1)!(30−r)!(31−r)30!=30r=1∑30(r−1)!(30−r)!(31−r)29!=30r=1∑30(30−r+1)29C30−r=30(r=1∑30(31−r)29C30−r+r=1∑3029C30−r)=30(29×228+229)=30(29+2)228=15×31×229=465(229)α=465