Use the following function rule to find f(9).
f(x) = 4 + 9x
f(9) =
?

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

Which is a true statement about an exterior angle of a triangle a. it is formed by two segments that are not sides of the triangle, b. it forms a linear pair with one of the interior angles of the triangle, c. it is complementary to one of the interior angles of the triangle. d. it is formed by two segments that are sides of the triangle.

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?