How to find the domain

Question

Find the domain of y=1/x+3 = -9

Answer 1

Please use parentheses.  I assume you really meant

 

y = 1/(x + 3)

 

The domain is all real numbers except where the denominator is zero, which is at x = -3.  In interval notation, the domain is (-∞, -3) ∪ (-3, ∞).