We are given the following function
We are asked to find the negative interval of this function.
A negative interval means that where the y values of the function are negative.
Let us have a look at the graph of this function.
As you can see,
For x = 0, the interval is positive.
For x = 1 and x = -1 the y value is 0 (we don't consider 0 as either positive or negative that's why 0 is not included in the negative or positive interval)
The y values of the function are negative for
x > 1 and x < -1
Therefore, the negative interval of the function y = x² + 1 is
[tex]1