For a given dataset, you fix the intercept of a linear regression model to be $\beta_0 = 10$. The sum of squared errors (SSE) can then be written as a function of the slope $\beta_1$: $SSE(\beta_1) = \sum_{i=1}^n (y_i - 10 - \beta_1 x_i)^2$. What is the geometric shape of this function $SSE(\beta_1)$, and what does its vertex represent?