Find Decreasing Intervals: Analyzing y = (x+8)² - 1

The function given is $y = (x+8)^2 - 1$, which is in vertex form. The vertex of this parabola is at $(-8, -1)$.

Since the coefficient of $(x+8)^2$ is positive ($+1$), the parabola opens upwards. This means that the function is decreasing to the left of the vertex.

In mathematical terms, the function is decreasing when $x$ is less than the vertex $x$-coordinate, $x = -8$.

Therefore, the function is decreasing for the interval $x < -8$.