f1 = @(x) ( sqrt( 1 + x ) - 1 ) ./ x;
f2 = @(x) 1 ./ ( sqrt( 1 + x ) + 1 );
f3 = @(x) 0.5 - x / 8 + x.^2 / 16 - 5 / 128 * x.^3;

values_f1 = []; values_f2 = []; values_f3 = [];

for k = 10 : 2 : 16
    values_f1 = [ values_f1, f1( 10^( -k ) ) ];
    values_f2 = [ values_f2, f2( 10^( -k ) ) ];
    values_f3 = [ values_f3, f3( 10^( -k ) ) ];
end

values_f1, values_f2, values_f3

X = 10.^-( 10 : 2 : 16 );

f1(X), f2(X), f3(X)

% ans =
% 
%     0.5000    0.5000    0.4885         0
% 
% 
% ans =
% 
%     0.5000    0.5000    0.5000    0.5000
% 
% 
% ans =
% 
%     0.5000    0.5000    0.5000    0.5000