f and t have a different number of elements. Then f .* t is not defined.
You did not tell us, what you want to achieve, but perhaps transposing one of the vectors will do what you want:
g = dot(cos(2*pi * f .* t.'), sin(2 * pi * f .* t.'));
% ^^ ^^
Try this:
x = 1:3
y = 4:7
x .* y % error
x .* y.' % matrix
