A point is on a graph if it's coordinates verify the
equation of the graph.
We'll use this rule to determine the
equationof the parabola.
We'll write the standard equation
of a parabola:
y = ax^2 +bx +
c
Since (1,0) is on the parabola, we'll
have:
0 = a + b + c
We'll use
symmetric property and we'll get:
a + b + c = 0
(1)
Since (2,2) is on the parabola, we'll
have:
4a + 2b + c = 2
(2)
Since (3,10) is on the parabola, we'll
have:
9a + 3b + c = 10
(3)
We'll subtract (1) from (2) and we'll
get:
4a + 2b + c - a - b - c =
2-0
We'll combine like
terms:
3a + b = 2 (4)
We'll
subtract (1) from (3) and we'll get:
9a + 3b + c - a - b -
c = 10 - 0
We'll combine like
terms:
8a + 2b = 10 (5)
We'll
multiply (4) by -2:
-6a - 2b = -4
(6)
We'll add (6) to (5):
8a +
2b - 6a - 2b = 10 - 4
We'll combine and eliminate like
terms:
2a = 6
We'll divide by
2:
a =
3
We'll substitute a in
(4):
9 + b = 2 (4)
We'll
subtract 9 both sideS:
b = 2 -
9
b =
-7
We'll substitute a and b in
(1):
a + b + c = 0
3 - 7 + c =
0
-4 + c = 0
We'll add
4:
c =
4
The equation of the parabola
is:
y = 3x^2 - 7x +
4
No comments:
Post a Comment