Question 118862: What are the procedures to write a quadratic equation in vertex form?
Found 2 solutions by MathLover1, Edwin McCravy: Answer by MathLover1(20849) (Show Source): Answer by Edwin McCravy(20054) (Show Source):
You can put this solution on YOUR website! What are the procedures to write a quadratic equation in vertex form?
First of all, learn what the vertex form is,
and how to graph the parabola from that form:
The vertex form of
y = a(x - h)² + k
has vertex (h, k) and goes through the two points,
(h-1,k+a) and (h+1,k+a)
Example 1:
Suppose you started with
y = 2x² - 12x + 22
1. Factor the coefficient of x² out of the first
two terms, using a bracket, so you can put
parentheses inside of it:
y = 2[x² - 6x] + 22
2. Out to the side or on scratch paper, complete
the square by:
(a) Multiplying the coefficient of x by .
-6( ) = -3
(b) Squaring the result of (a).
(-3)² = +9
3. Add, then subtract, the result of 2.(b) inside
the brackets:
y = 2[x² - 6x + 9 - 9] + 22
4. Factor the binomial consisting of the first three
terms inside the brackets:
y = 2[(x - 3)(x - 3) - 9] + 22
5. If everything has gone right, the two factors of
that binomial will be the same, making it a
perfect square, so write it as a binomial squared:
y = 2[(x - 3)² - 9] + 22
6. Remove the brackets by distributing, remembering
to leave the parentheses intact:
y = 2(x - 3)² - 18 + 22
7. Combine the last two numerical terms:
y = 2(x - 3)² + 4
Compare that to
y = a(x - h)² + k
Then a = 2, h = 3 and k = 4. So by the
above, the graph has vertex (h, k) = (3,4) and
it goes through the two points,
(h-1,k+a) = (3-1,4+3) = (2,7)
and
(h+1,k+a) = (3+1,4+3) = (4,7)
So plot those three points:
and draw a U-shaped graph through them, called a parabola:
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Example 2:
Suppose you started with
y = -x² - 8x - 13
y = -(x + 4)² + 3
1. Factor the coefficient of x² out of the first
two terms, using a bracket, so you can put
parentheses inside of it:
y = -1[x² + 8x] - 13
2. Out to the side or on scratch paper, complete
the square by:
(a) Multiplying the coefficient of x by .
8( ) = +4
(b) Squaring the result of (a).
(+4)² = +16
3. Add, then subtract, the result of 2.(b) inside
the brackets:
y = -1[x² + 8x + 16 - 16] - 13
4. Factor the binomial consisting of the first three
terms inside the brackets:
y = -1[(x + 4)(x + 4) - 16] - 13
5. If everything has gone right, the two factors of
that binomial will be the same, making it a
perfect square, so write it as a binomial squared:
y = -1[(x + 4)² - 16] - 13
6. Remove the brackets by distributing, remembering
to leave the parentheses intact:
y = -1(x + 4)² + 16 - 13
7. Combine the last two numerical terms:
y = -1(x + 4)² + 3
Compare that to
y = a(x - h)² + k
Then a = -1, h = -4 and k = 3. So by the
above, the graph has vertex (h, k) = (-4,3) and
it goes through the two points,
(h-1,k+a) = ( -4-1, 3+(-1) ) = (-5,2)
and
(h+1,k+a) = ( -4+1, 3+(-1) ) = (-3,2)
So plot those three points:
and draw a U-shaped graph through them, called a parabola. This is
an upside down U graph which will always be the case whenever "a",
the coefficient of x² is a negative number:
Edwin
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