Text description - screencast for exercise 3

[The narrator reads out the onscreen text.]

NARRATOR: Exercise three. A parabola has vertex (1, 3) and passes through the point (3, 11). Find its equation. We know that an equation given in turning point form - that is in the form y = a(x - h) all squared plus k - has a vertex at (h, k). So in this case, with the vertex at (1, 3), the equation will be of the form y = a(x - 1) all squared, + 3. So with the equation in this form, the point (3, 11) can be used to calculate a. So we substitute the point (3, 11) in - that is, when x = 3, y = 11.

[The equation reads 11 equals a times (3 minus 1) all squared, plus 3. So 11 equals 4a plus 3. So 8 equals 4a. So a equals 2.]

NARRATOR: In simplifying and solving for a, we find that a is equal to 2. So therefore the equation of the parabola which has a vertex at (1, 3) and passes through the point (3, 11) is y = 2(x-1) all squared, + 3.