For this specific problem:
f(x) = x4, a= 2 and x= 1.999
Going with this, 1.9994 = 24 + 4 * (23) * (- 0.001) = 15.968
I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.