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Concrete mathematics : a foundation for computer science

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A ANSWERS TO EXERCISES 513<br />

5.16 This is just (;!a)! (2b)! (2c)!/(a+ b)! (b+c)! (c+ a)! times (5.2g), if we<br />

write the summands in terms of factorials.<br />

27/2)<br />

5.17 ( = (;;)/22”; (2-/2) = (;;)/24”; so (2nn’/2) = 22n(2-/2).<br />

5.18 (:;)(,"k",k)i33k.<br />

5.19 Bl .t(-2) ’ := tkzO (kP’,“P’) (-l/(k ~ tk - 1)) (-.z)~, by (5.60), and<br />

this is tkaO (tt)(l/(tk- k+ 1))~~ = ‘BH,(z).<br />

5.20 It equals F(-al, . ,-a,; -bl, . . . ,-b,; (-l)mfnz); see exercise 2.17.<br />

5.21 lim,,,(n + m)c/nm = 1.<br />

5.22 Multiplying and dividing instances of (5.83) gives<br />

(-l/2)!<br />

x!(x-l/2)!<br />

by (5.34) and (5.36). Also<br />

1/(2x)! = lim 2n+2x<br />

n--c% 2n<br />

= &c ("n'") (n+xc1'2)n 2r/(n-i'2)<br />

2n + 2x n--2X<br />

= lim<br />

n+cc ( 2n ><br />

’<br />

( )<br />

(2n) -2x .<br />

Hence, etc. The Gamma function equivalent, incidentally, is<br />

T(x) l-(x + ;, = r(2x) r(;)/22x- ’<br />

5.23 (-l)"ni, see (5.50).<br />

5.24 This sum is (1:) F( ",~~"ll> = (fz), by (5.35) and (5.93).<br />

5.25 This is equivalent to the easily proved identity<br />

a’ (a+llEemb<<br />

( a - b ) - - = oP<br />

(b + II)” (b+l)k bk<br />

as well as to the operator <strong>for</strong>mula a - b = (4 + a) - (4 + b).<br />

Similarly, we have<br />

(al - a21 F<br />

al,a2,a3, . . . . am<br />

bl, . . . , bn<br />

= alF al+l,a2,a3,...,am<br />

bl, . , b,<br />

13 -wF(<br />

al,a2+l,a3,...,am

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