Monday, January 17, 2011

A parabolla passes through the points (1,0), (2,2), (3,10). Deterine its equation.

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

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