Nick:
You only need Est, not Est(1) because Est is not an array - it's a scalar. Also, don't assign Est to x as the first line because there is no x yet. And you need to initialize Est to x, not 1, AFTER you get x.
N=input('Please enter how many terms you would like to go out:')
x=input('Please enter the angle in radians:')
Est=x;
for k= 2:N
termK = (-1)^(k-1)*x^(2*k-1)/factorial(2*k-1);
Est = Est + termK;
fprintf('Term %d = %.6f, so now Est = %.6f\n', k, termK, Est);
end
fprintf('The final Estimated Value = %.6f\n', Est)
fprintf('Actual Value of sin(%.6f) = %0.6f\n', x, sin(x))
fprintf('Difference is %0.6f\n', Est-sin(x))
