=========================================================
Explanation:
Draw two parallel number lines as shown in the diagram below. Make sure the numbers line up.
The first number line has the interval [0,7] which is the same as writing 0 ≤ x ≤ 7
We have closed circles at 0 and 7. Then there's shading in between those endpoints.
Similarly, the other interval [-2, 5] represents -2 ≤ x ≤ 5. It has shading between the closed circles at -2 and 5.
The red dashed lines represent the portions where the two number lines overlap. This is from x = 0 to x = 5
The sub-interval 0 ≤ x ≤ 5 is found in both domains, and hence it's the domain of f+g
That turns into the interval notation of [0, 5]