表达式4: "y" equals left parenthesis, left parenthesis, StartFraction, left parenthesis, nCr left parenthesis, "x" minus 1 , "d" minus 1 , right parenthesis times nCr left parenthesis, 39 minus left parenthesis, "x" minus 1 , right parenthesis , 5 minus "d" , right parenthesis , right parenthesis Over nCr left parenthesis, 39 , 4 , right parenthesis , EndFraction , right parenthesis plus left parenthesis, StartFraction, left parenthesis, nCr left parenthesis, "x" minus 1 , "d" , right parenthesis times nCr left parenthesis, 39 minus left parenthesis, "x" minus 1 , right parenthesis , 5 minus left parenthesis, "d" plus 1 , right parenthesis , right parenthesis , right parenthesis Over nCr left parenthesis, 39 , 4 , right parenthesis , EndFraction , right parenthesis , right parenthesis times .3 3 7y=nCrx−1,d−1·nCr39−x−1,5−dnCr39,4+nCrx−1,d·nCr39−x−1,5−d+1nCr39,4·.337
4
"x"x
left parenthesis, left parenthesis, StartFraction, left parenthesis, nCr left parenthesis, "x" minus 1 , "d" minus 1 , right parenthesis times nCr left parenthesis, 39 minus left parenthesis, "x" minus 1 , right parenthesis , 5 minus "d" , right parenthesis , right parenthesis Over nCr left parenthesis, 39 , 4 , right parenthesis , EndFraction , right parenthesis plus left parenthesis, StartFraction, left parenthesis, nCr left parenthesis, "x" minus 1 , "d" , right parenthesis times nCr left parenthesis, 39 minus left parenthesis, "x" minus 1 , right parenthesis , 5 minus left parenthesis, "d" plus 1 , right parenthesis , right parenthesis , right parenthesis Over nCr left parenthesis, 39 , 4 , right parenthesis , EndFraction , right parenthesis , right parenthesis times .3 3 7nCrx−1,d−1·nCr39−x−1,5−dnCr39,4+nCrx−1,d·nCr39−x−1,5−d+1nCr39,4·.337
