Given the following function f(x)=-x^2-10x. Find the domain, range and decreasing intervals?

Answer 1

as with all polynomials, the domain is all real numbers.

f(x) = -x(x+10)
This is a parabola opening downwards. Its maximum occurs midway between its root, at x = -5
f(-5) = 25
so, the range is y <= 25

Since its maximum is at x = -5, it decreases for x in (-5,oo).