Let f(x)= 5/x and g(x)=2x^2+5x what two numbers are not in the domain of f o g?

Fog means f(x) compsed with g(x) or f(g(x)

so put g(x) for the x in f(x)

f(g(x))=5/(g(x))
f(g(x))=5/(2x^2+5x)

domian is the numbers you can use
basically it is not in the domain if it makes the function undefined
some things not in domain are values that make the function divide by zero and/or take the square root of a negative number

so divide by 0
set denomenator to 0 and solve for restricted values
0=2x^2+5x
0=x(2x+5)
0=x or
0=2x+5
-5=2x
-2.5=x

the 2 values not in the domain of f o g are 0 and -2.5