problem: What is the domain of the function $$k(y) = \frac{1}{2y+1}~?$$ Express your answer in interval notation.
solution: The fraction $\frac{1}{2y+1}$ fails to be defined only if the denominator is zero. This occurs when $y$ is the solution of the equation $$2y+1=0,$$ which is $y=-\frac 12$. Thus the domain of $k(y)$ is $$\boxed{\left(-\infty,-\frac 12\right)\cup \left(-\frac 12,\infty\right)}.$$