Answer:
(-∞, -5) ∪ (-2, 2)
Step-by-step explanation:
A function is "decreasing" where its slope is negative. That is, the curve goes downward to the right. The parts of the curve with negative slope are marked in the attachment with blue arrows.
The intervals for which the function is decreasing are bounded by either of (a) the domain bounds, or (b) critical points, where the slope is either zero or undefined.
Here, the slope is negative for -∞ < x < -5, and for -2 < x < 2. Note that the "or equal to" case is excluded from these intervals, because the slope is actually 0 at the critical points; it is not negative.
In interval notation, these open intervals are written ...
(-∞, -5) ∪ (-2, 2)
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Additional comment
The function is "increasing" where it has positive slope. The other two intervals of this graph are where the function is increasing:
(-5, -2) ∪ (2, ∞)
