Respuesta :
Answer:
The given equations are;
y = a·(x - h)² + k or y = a·x² + b·x + c
We have;
(x - h)² = 4·p·(y - k),
Where;
(h, k) are the x, and y coordinates of the vertex
p = The distance from the focus to vertex distance;
Comparing, we have;
y - k = a·(x - h)²
(y - k)/a = (x - h)²
(x - h)² = 4·p·(y - k)
4·p·(y - k) = (x - h)²
∴ 4·p = 1/a
p = 1/(4·a)
Therefore, the focus to vertex distance inversely proportional to the value of a
The distance of every point on the parabola is equidistant from the directrix and the focus
Therefore, the equation of the directrix is y = k - p
For example, we have;
y = 2·x² + 3·x + 1
h = -b/2a = -3/4
k = (4ac - b²)/4a = (4×2×1 - 3²)/(4×2) = -1/8
The coordinate of the focus is (h, k + p) = (-3/4, -1/8 + 1/8) = (-3/4, 0)
The directrix, y = k - p = -1/8 - 1/8 = -1/4
For a point x = 2, we have, y = 2·2² + 3·2 + 1 = 15
The coordinate of the point is (2, 15)
The distance of the point from the directrix = 15 - (-1/4) = 15 + 1/4 = 15.25
The distance of the point from the focus is √((2 - (-3/4))² + (15 - 0)²) = 15.25
Therefore, all points on the parabola have equal distances from the focus and the directrix
Step-by-step explanation:
