mathematical symbol, what does the open circle mean?

Question

What does the circle in d) and e) means?

In this exercise, I have to find inverse matrix. $h:\mathbb{R}^3 \to \mathbb{R}^3$ is given by $$h(x,y,z) = (4x+y,x+z,-2x+3y+z)$$

(d) $g \circ h$

(e) $h \circ g$

Answer 1

It means composition, for Instance $g(x)=x^2$ and $f(x)=-1/x$. So $g(f(x)) = (-1/x)^2 = \frac{1}{x^2}$ and $f(g(x))= \frac{-1}{x^2}$