3. STRATEGIC
INTERVENTION
MATERIAL
Solving Quadratic Equation
by Completing the Square
Least Mastered Competency
* Solving Quadratic Equation by Completing a Square
Sub Tasks:
*Identifying quadratic equation
*Determining a perfect square trinomial
*Expressing Perfect Square trinomial as a square of a binomial
*Solving quadratic equation by completing the square.
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4. GUIDE CARD
A quadratic equation in one variable is a mathematical sentence of
degree 2 that can be written in the following form;
𝑎𝑥2
+ 𝑏𝑥 + 𝑐 = 0, 𝑤ℎ𝑒𝑟𝑒 𝑎, 𝑏, 𝑎𝑛𝑑 𝑐
𝑎𝑟𝑒 𝑟𝑒𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟𝑠 𝑎𝑛𝑑 𝑎 ≠ 0.
In the equation, 𝑎𝑥2, is the quadratic term, 𝑏𝑥 is the linear term, and 𝑐
is the constant term.
Example:
2𝑥2
+ 5x + 3 = 0
𝑎 = 2, 𝑏 = 5, 𝑐 = 3
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5. Activity 1. Quadratic or Not
Determine the given expression as quadratic or
not. Write Q if it quadratic and NQ if it is not.
__________1. 𝑥 + 5 = −2
__________2. 𝑥2
− 5 = 𝑥
__________3. −2𝑥2
=0
__________4. 𝑥 − 10 = 3𝑥
__________5. 𝑥3
+ 𝑥2
= −1
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6. On Quadratic Equation
A quadratic equation in one variable is a mathematical sentence of degree 2 that
can be written in the following form;
𝑎𝑥2
+ 𝑏𝑥 + 𝑐 = 0, 𝑤ℎ𝑒𝑟𝑒 𝑎, 𝑏, 𝑎𝑛𝑑 𝑐
𝑎𝑟𝑒 𝑟𝑒𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟𝑠 𝑎𝑛𝑑 𝑎 ≠ 0.
In the equation, 𝑎𝑥2
, is the quadratic term, 𝑏𝑥 is the linear term, and 𝑐 is the
constant term.
Why do you think a must
not be equal to zero?
Example:
2𝑥2
+ 5x + 3 = 0
𝑎 = 2, 𝑏 = 5, 𝑐 = 3
Why do you think a must not be
equal to zero? ans
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7. 𝒂𝒙 𝟐 + 𝒃𝒙 + 𝒄 = 𝟎
Substituting 𝒂 = 𝟎 in the equation
will yield a linear equation. So 𝒂 must
not be equal to zero
𝟎𝒙 𝟐 + 𝒃𝒙 + 𝒄 = 𝟎
𝒃𝒙 + 𝒄 = 𝟎
illustration
The derived equation is in first degree
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8. Activity 2: Am I a Perfect Square Trinomial or Not?
Determine each of the following whether it is a
perfect square trinomial or not. Write PST if it is
a perfect square trinomial and NPST if it is not.
_________1. 𝑥2
+ 2𝑥 − 2
_________2. 𝑥2
+ 4𝑥 + 4
_________3. 4𝑥2
− 8𝑥 + 2
_________4. 𝑥2
− 6𝑥 − 9
_________5. 2𝑥2
− 4𝑥 + 4
How do you
describe a
perfect square
trinomial?
How do you
describe a
perfect square
trinomial?
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9. Perfect Square Trinomial
First and last terms are perfect square.
Middle term is twice the product of the square
root of the first and last terms.
Example:
𝑥2
+ 4𝑥 + 4 𝑚𝑖𝑑𝑑𝑙𝑒 𝑡𝑒𝑟𝑚
4𝑥 = 𝑥2 ∙ 4
first and last term
(perfect squares)
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10. Activity 3. Transform Me!
Express each of the given trinomial as a square
of a binomial.
1. 𝑥2
− 4𝑥 + 4 ∶ ___________
2. 𝑦2
− 12𝑦 + 36: ___________
3. 𝑧2
− 10𝑧 + 25: ___________
4. 𝑤2
+ 16𝑤 + 64: ___________
5. 𝑎2
+ 14𝑎 + 49: ______________
How to transform a
PST to a square of
a binomial?
ans
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13. How to solve QE using completing the square
method?
Another method of solving quadratic
equation is by completing the square. This
method involves transforming the quadratic
equation 𝑎𝑥2
= 𝑏𝑥 + 𝑐 = 0 into the form (𝑥 −
ℎ)2
= 𝑘, where 𝑘 ≥ 0.
What are the steps in solving
QE by completing the
square?
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14. Steps in solving QE by
completing the square
1. Divide both sides of the equation by a then simplify.
2. Write the equation such that the terms with variables are on
the left side of the equation and the constant term is on the
right side.
3. Add the square of one-half of the coefficient of x on both
sides of the resulting equation.
4. Express the perfect square trinomial on the left side of the
equation as a square of a binomial.
What happens to the left side of the equation? ans
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16. Steps in solving QE by
completing the square: Cont…
5. Solve the resulting QE by extracting the
square root. Add the square of one-half of the
coefficient of x on both sides of the resulting
equation.
6. Solve the resulting linear equation.
7. Check the solution obtained against the
original equation.
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17. Example: Solve the quadratic equation
𝑥2
+ 3𝑥 − 10 = 0 by completing the square.
Solution: Divide both sides of the equation by 2 then simplify.
2𝑥2
+ 8x − 10 = 0
2𝑥2+8𝑥−10=0
2
=𝑥2
+ 4𝑥 − 5 = 0
Add 5 to both sides of the equation, then simplify.
𝑥2
+ 4𝑥 − 5 = 0 𝑥2
+ 4𝑥 − 5 + 5 = 0 + 5
𝑥2 + 4𝑥 = 5
Add to both sides of the equation the square of one-half
of 4.
1
2
4 = 2 22=4.
𝑥2 + 4𝑥 = 5 → 𝑥2 + 4𝑥 + 4 = 5 + 4
𝑥2 + 4𝑥 + 4 = 9
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26. Use the figure as a guide. Let x be the length of a side of the square piece of
metal. The box will have a height of 1 foot and its square base will have x-2
as the length of a side. The volume of the box is therefore
Length x width x height = 𝟏 𝒙 − 𝟐 𝒙 − 𝟐 = 𝒙 − 𝟐 𝟐
Since the volume of the box is to be 4 cubic feet,
𝒙 − 𝟐 𝟐 = 𝟒
𝒙 − 𝟐 = ±𝟐
𝒙 − 𝟐 = −𝟐
𝒙 = 𝟎
𝒙 − 𝟐 = 𝟐
𝒙 = 𝟒 or1
1
x
x-2 Discard the solution 𝒙 = 𝟎
because length cannot be zero.
Therefore, the sheet metal should be
4 feet by 4 feet
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27. Answer key
Activity 1. Quadratic or Not
Activity 2: Am I a Perfect Square
Trinomial or Not?
Activity 3. Transform Me!
1. 𝒙 − 𝟐 𝟐
2. 𝒚 − 𝟔 𝟐
3. 𝒛 − 𝟓 𝟐
4. ( 𝒘 +
Assessment Card 1
Assessment Card 2
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