Lesson: Completing the Square
To solve quadratic formulas
To solve quadratic formulas
there are 3 basic methods
To solve quadratic formulas
there are 3 basic methods
1. Factoring
To solve quadratic formulas
there are 3 basic methods
1. Factoring
2. Quadratic Formula
To solve quadratic formulas
there are 3 basic methods
1. Factoring
3. Completing the square
2. Quadratic Formula
Completing the square involves several steps
Completing the square involves several steps
1. get c by itself
Completing the square involves several steps
1. get c by itself
2. Divide by a
Completing the square involves several steps
1. get c by itself
2. Divide by a
3. Add (b/2)2 to both sides
Completing the square involves several steps
1. get c by itself
2. Divide by a
4. Factor (put in exponential form)
3. Add (b/2)2 to both sides
Completing the square involves several steps
1. get c by itself
2. Divide by a
4. Factor (put in exponential form)
3. Add (b/2)2 to both sides
5. Solve
Completing the square involves several steps
1.
2.
3.
4.
5.
get c by itself
?
Divide by a
?
Factor (put in exponential form)
?
Add (b/2)2 to both sides
?
Solve
?
Let's do an example
Let's do an example
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's do an example
x2 - 8x -20 = 0
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
a = 1
Let's do an example
x2 - 8x -20 = 0
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
a = 1
Let's do an example
x2 - 8x -20 = 0
b = -8
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
a = 1
Let's do an example
x2 - 8x -20 = 0
b = -8
c = -20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
a
?
3x2 -5x +7 = 0
b
?
c
?
-2x2 +8x -4 = 0
c =
b =
a =
Let's do an example
First we get c by itself
x2 - 8x -20 = 0
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's do an example
First we get c by itself
x2 - 8x -20 = 0
+20
+20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's do an example
First we get c by itself
x2 - 8x -20 = 0
x2 - 8x = 20
+20
+20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's do an example
Now divide everything by a
x2 - 8x -20 = 0
x2 - 8x = 20
+20
+20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's do an example
Now divide everything by a
but since a is 1, we divide everything by 1
x2 - 8x -20 = 0
x2 - 8x = 20
+20
+20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's do an example
Now divide everything by a
but since a is 1, we divide everything by 1
x2 - 8x -20 = 0
which means the equation doesn't change
x2 - 8x = 20
+20
+20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's do an example
Then we add (b/2)2 to both sides
x2 - 8x -20 = 0
x2 - 8x = 20
+20
+20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's do an example
Then we add (b/2)2 to both sides
Since b = -8, then we will add 16 to both sides
x2 - 8x -20 = 0
x2 - 8x = 20
+20
+20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's do an example
Then we add (b/2)2 to both sides
Since b = -8, then we will add 16 to both sides
x2 - 8x -20 = 0
x2 - 8x = 20
+20
+16
+16
+20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's do an example
Then we add (b/2)2 to both sides
Since b = -8, then we will add 16 to both sides
x2 - 8x -20 = 0
x2 - 8x +16 = 36
x2 - 8x = 20
+20
+16
+16
+20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Then, factor the left side
Let's do an example
x2 - 8x -20 = 0
x2 - 8x +16 = 36
x2 - 8x = 20
+20
+16
+16
+20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Then, factor the left side
Let's do an example
(x - 4)(x - 4) = 36
x2 - 8x -20 = 0
x2 - 8x +16 = 36
x2 - 8x = 20
+20
+16
+16
+20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Then, factor the left side
Let's do an example
(x - 4)(x - 4) = 36
x2 - 8x -20 = 0
x2 - 8x +16 = 36
put in exponential form
x2 - 8x = 20
+20
+16
+16
+20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Then, factor the left side
Let's do an example
(x - 4)(x - 4) = 36
x2 - 8x -20 = 0
x2 - 8x +16 = 36
put in exponential form
x2 - 8x = 20
(x - 4)2 = 36
+20
+16
+16
+20
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's do an example
(x - 4)(x - 4) = 36
x2 - 8x -20 = 0
x2 - 8x +16 = 36
x2 - 8x = 20
(x - 4)2 = 36
+20
+16
+16
+20
Last, solve the equation
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's do an example
(x - 4)(x - 4) = 36
x2 - 8x -20 = 0
x2 - 8x +16 = 36
x2 - 8x = 20
(x - 4)2 = 36
+20
+16
+16
+20
Last, solve the equation
First square root
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
both sides
Let's do an example
(x - 4)(x - 4) = 36
x2 - 8x -20 = 0
x2 - 8x +16 = 36
x2 - 8x = 20
(x - 4)2 = 36
x - 4 = ±6
+20
+16
+16
+20
Last, solve the equation
First square root
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
both sides
Let's do an example
(x - 4)(x - 4) = 36
x2 - 8x -20 = 0
x2 - 8x +16 = 36
x2 - 8x = 20
(x - 4)2 = 36
x - 4 = ±6
+4
+20
+16
+4
+16
+20
Last, solve the equation
First square root
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
both sides
Let's do an example
(x - 4)(x - 4) = 36
x2 - 8x -20 = 0
x2 - 8x +16 = 36
x2 - 8x = 20
(x - 4)2 = 36
x - 4 = ±6
+4
+20
+16
+4
+16
+20
x = +6 + 4
Last, solve the equation
First square root
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
both sides
Let's do an example
(x - 4)(x - 4) = 36
x2 - 8x -20 = 0
x2 - 8x +16 = 36
x2 - 8x = 20
(x - 4)2 = 36
x - 4 = ±6
+4
+20
+16
+4
+16
+20
x = +6 + 4
Last, solve the equation
x = 10
First square root
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
both sides
Let's do an example
(x - 4)(x - 4) = 36
x2 - 8x -20 = 0
x2 - 8x +16 = 36
x2 - 8x = 20
(x - 4)2 = 36
x - 4 = ±6
+4
+20
+16
+4
+16
+20
x = +6 + 4
Last, solve the equation
x = 10
First square root
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
both sides
x = -6 + 4
Let's do an example
(x - 4)(x - 4) = 36
x2 - 8x -20 = 0
x2 - 8x +16 = 36
x2 - 8x = 20
(x - 4)2 = 36
x - 4 = ±6
+4
+20
+16
+4
+16
+20
x = +6 + 4
Last, solve the equation
x = 10
First square root
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
both sides
x = -6 + 4
x = -2
Let's do an example
(x - 4)(x - 4) = 36
x2 - 8x -20 = 0
x2 - 8x +16 = 36
x2 - 8x = 20
(x - 4)2 = 36
x - 4 = ±6
+4
+20
+16
+4
+16
+20
x = +6 + 4
Last, solve the equation
x = 10
First square root
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
both sides
x = -6 + 4
x = -2
Let's try a harder one
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's try a harder one
2x2 + 3x -5 = 0
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's try a harder one
2x2 + 3x -5 = 0
First get c by itself
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's try a harder one
2x2 + 3x -5 = 0
+5
+5
First get c by itself
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's try a harder one
2x2 + 3x -5 = 0
2x2 + 3x = 5
+5
+5
First get c by itself
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's try a harder one
2x2 + 3x -5 = 0
2x2 + 3x = 5
+5
+5
Then divide by a
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's try a harder one
2x2 + 3x -5 = 0
2x2 + 3x = 5
2
+5
2
+5
2
Then divide by a
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
2
3
2
+5
2
2
5
+5
2
Then divide by a
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
2
3
2
+5
2
2
5
+5
2
Now add (b/2)2 to both sides
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
+
2
16
3
2
9
+5
+
2
2
16
5
9
+5
2
Now add (b/2)2 to both sides
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
x2 +      x +      =
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
+
3
2
2
16
3
2
9
+5
+
16
2
9
2
16
5
9
+5
2
16
49
Now add (b/2)2 to both sides
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
x2 +      x +      =
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
+
3
2
2
16
3
2
9
+5
+
16
2
9
2
16
5
9
+5
2
16
49
Now we factor
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
x2 +      x +      =
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
+
3
2
2
16
3
2
9
+5
+
16
2
9
2
16
5
9
+5
2
16
49
Now we factor
Unfortunately the fractions
make it hard to factor
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
x2 +      x +      =
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
+
3
2
2
16
3
2
9
+5
+
16
2
9
2
16
5
9
+5
2
16
49
So we will just set it up like this
(x         )2 =
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
16
49
x2 +      x +      =
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
+
3
2
2
16
3
2
9
+5
+
16
2
9
2
16
5
9
+5
2
16
49
Use the first sign
(x         )2 =
+
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
16
49
x2 +      x +      =
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
+
3
2
2
16
3
2
9
+5
+
16
2
9
2
16
5
9
+5
2
16
49
Square root 
(x         )2 =
+
3
4
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
16
9
16
49
x2 +      x +      =
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
+
3
2
2
16
3
2
9
+5
+
16
2
9
2
16
5
9
+5
2
16
49
(x         )2 =
+
3
4
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
16
49
Then we solve
x2 +      x +      =
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
+
3
2
2
16
3
2
9
+5
+
16
2
9
2
16
5
9
+5
2
16
49
(x         )2 =
+
3
4
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
16
49
Then we solve
x2 +      x +      =
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
+
3
2
2
16
3
2
9
+5
+
16
2
9
2
16
5
9
+5
2
16
49
(x         )2 =
x +         = ±
+
3
4
4
3
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
16
49
7
4
x2 +      x +      =
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
+
3
2
2
16
3
2
9
+5
+
16
2
9
2
16
5
9
+5
2
16
49
x = -
(x         )2 =
x +         = ±
+
4
3
3
4
4
3
+
7
4
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
16
49
x = -
7
4
4
3
-
7
4
x2 +      x +      =
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
+
3
2
2
16
3
2
9
+5
+
16
2
9
2
16
5
9
+5
2
16
49
x = -
(x         )2 =
x = 1
x +         = ±
+
4
3
3
4
4
3
+
7
4
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
16
49
x = -
7
4
x = -2.5
4
3
-
7
4
x2 +      x +      =
Let's try a harder one
2x2 + 3x -5 = 0
x2 +   x =
2x2 + 3x = 5
+
3
2
2
16
3
2
9
+5
+
16
2
9
2
16
5
9
+5
2
16
49
x = -
(x         )2 =
x = 1
x +         = ±
+
4
3
3
4
4
3
+
7
4
1. Get c by itself
4. Factor (expontential form)
2. Divide by a
3. Add (b/2)2 to both sides
5. Solve
16
49
x = -
7
4
x = -2.5
4
3
-
7
4
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