This is now, what, the third or 4th time you asked this question? The first few times, it was explicitly about your homework assignment. But the answer is simple, though not always simple to accomplish.
- Evaluate the function at some pair of points.
- If the function has opposite signs at those two points, then you are done.
- If the function has the SAME sign at both points, then search for a new point which has the opposite sign from the one you already have. This is not lways trivial to accomplish, but there is no alternative.
You can accelerate the search above by evaluating the function at multiple points at once if possible. If you do so, AND if there exists any pair of points that have the opposite sign on the function value, then again you have found a bracket that must contain the root.
Again, it is not always possible to find some pair of points that bracket a root, since one can always create a black box function for which it is arbitrarily difficult to locate a bracket.
Now please stop asking this same question. And no, I will not write the code for you, since this is certainly a homework assignment based on the last three identical questions you asked.