a = bin2dec('00010101');
b = bin2dec('00010010');
c = bin2dec('11000101')
x = -10:50; % Nicer and faster than: [(-10):1:50]
y1 = (-b.*((x-a).^2))+c;
y2 = (c.*x)-a;
plot(x, y1);
hold on
plot(x, y2);
You need to specify x in the plot() command, otherwise Matlab assumes it is 1:length(y).
See http://www.mathworks.com/matlabcentral/answers/35676-why-not-use-square-brackets for the unneeded square brackets.
