Why aren't voluntary samples usually representative of the population?

Given that (x-3) is a factor of f(x)=x^3+ax^2-x-6, find a and hence the number of real roots or the equation f(x)=0

Which is the equation of an ellipse with directrices at x = ±4 and foci at (2, 0) and (−2, 0)?

Consider the functions below. function 1 function 2 function 3 select the statement which is true about the functions over the interval [1, 2] a b function 3 has the highest average rate of change function 2 and function 3 have the same average rate of change. function and function 3 have the same average rate of change function 2 has the lowest average rate of change d.