I wrote following code but it is not returning zero. fzero returns initial values. Is there anything I did wrong?

alp=0.05; x=3; n=25;

syms k a;

ftest=@(a) 1-alp/2-.5*nchoosek(n,x)*a^x*(1-a)^(n-x) – symsum(nchoosek(n,k)*a^k*(1-a)^(n-k+1), k, 0, x-1);

fzero(ftest,0.02)

ans =

0.0200

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