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Ax BX +C 0 Ax BX +C 0: Grade 9 Summarized Module

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GRADE 9

SUMMARIZED MODULE

QUADRATIC EQUATION

III-MOST ESSENTIAL LEARNING COMPETENCIES

The learner illustrates quadratic equations. Solves quadratic equations by extracting the square
roots, factoring, completing the square and using the quadratic formula.

An equation that can be written in the form ax 2 +bx +c=0 , where a, b and c are real numbers
with a≠ 0, is a quadratic equation in general form. The name quadratic comes from “quad” meaning
square. If the quadratic equation is written ax 2 +bx +c=0 in which all the nonzero terms on the left side
equating to 0, it is said to be a quadratic equation in general form. A quadratic equation is called a second
degree equation because the left side is a polynomial of degree 2.

Here are more examples:

2 x2 +5 x +3=0 It is a quadratic equation in which a=2, b=5 and c


=3
x 2+ 3 x =0 You don’t usually write “1 x2” thus a=1, b=3 and 3
is not shown, because c=0
5 x+ 3=0 The term of degree 2 is missing, which means a=0.
By definition this equation can never be called
quadratic. It is a linear equation.

Illustrative examples

Write each of these quadratic equation in general form and identify the real numbers a, b and c.

1. m 2 +7 m−8=0

Solution

m 2 +7 m−8=0 it is already in general form, where a=1, b=7 and c= -8

2. 4 x2 −3 x =5

Solution
4 x2 −3 x −5=0 the equation in general form. Thus a=4, b=-3 and c=-5

SOLVING QUADRATIC EQUATIONS BY THE SQUARE ROOT

Example:

Solve for x: x 2=16

Solution:

Get all the terms on the same side by addition x 2−16=0


property of equality (difference of two squares)
By the addition property of equality 2
x =16
Extract the square root x=4,x= -4
List all the value of x. x={4,-4}

SOLVING QUADRATIC EQUATIONS BY FACTORING

Example:

Solve for x: x 2−x=6

Solution:

Here are the steps you should follow:

1. Move all terms to the same side of the equal sign, so x 2−x−6=0
the equation is set equal to 0. This places the equation in general form
2. Factor the algebraic expression (x-3)(x+2) are called factors. These are
the factors of the equation x 2−x−6 .
3. Set each factor equal to 0.this process is called the x-3=0; x+2=0
“zero product property”. If the product of two factors
equal to 0, then either one or both of the factors must
be 0.
4. Solve each resulting equation. x=3 and x= -2 are called roots. These are
the roots of the equation x 2−x−6=0

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