No. x2+5x is a polynomial, an algebraic expression or a formula, but it is not a function. It could be used to help define a function.
{(x,y) | y = x2 + 5x , x any real number} is a function
x2 + 5x - 120 can not be factored.
x2 + 5x + 6 = (x + 2)(x + 3)
2x + 5x = 7x
x2 - 5x + 6 = (x - 2)(x - 3)
(3x - 5x) + (x2 - 6x2) = -2x -5x2 = -x(2 + 5x)
x2 + 5x + 3 = 9 x2 + 5x - 6 = 0 (x + 6)(x - 1) = 0 x = -6 or x = 1
x2+5x+6 = (x+2)(x+3)
5x+x >100
5(x2 + x + 1)
x(x2+5x+6)
x2+5x-14 = (x+7)(x-2) when factored
x2+5x+6 = (x+2)(x+3) when factored because 2 and 3 are factors of 6