You may want to check your function, because it doesn't seem to have any (real) zeros:
f = @(n,I) n*210+(I.^2/n).*((((200-32*I).^2)/200)+32)-197;
figure
I = linspace(-100,100,5001);
y = f(1,I);
plot(I,y)
min(y)
But, the approach would be to define a function handle for f, as above, then set the value of n and apply fzero to the resulting function of one variable ( I ):
f = @(n,I) n*210+(I.^2/n).*((((200-32*I).^2)/200)+32)-197;
I0 = 0; % Make an initial guess
for n = 1:5
g = @(I) f(n,I); % Make a new function from f(n,I) with n fixed
I0 = fzero(g,I0) % Find zero, starting with previous result
end
