CHAPTER 4 : QUADRATIC EQUATIONS
4.1 Theorem
If a, b Ï R and ab = 0 then either a = 0 or b = 0
Corollary 1 : If a . b = 0 but a ¹ 0, then b = 0
Corollary 2 : If a . b . c = 0, a ¹ 0, b ¹ 0, then c = 0
Corollary 3 : If ab = ac, then either a = 0 or b = c
Example
Solution :
Example
Solution :  For what values of x is the expression x (3x  6 ) = 0 ? i.e. x (3x  6 ) = 0 Þ either x = 0 or 3x 6 = 0 i.e. x = 0 or 3x = 6 x = 2 Therefore, there are two values of x (viz, 0 and 2 ) that make the expression zero.
Solve (3x + 1 ) (x + 3) = (x  2) (x + 3) Transposing ( x + 3 ) ( 3x + 1 )  ( x  2 ) ( x + 3 ) = 0 i.e. ( x + 3 ) [ ( 3x + 1 )  ( x  2 ) ] = 0
i.e. ( x + 3 ) ( 3x + 1  x + 2 ) = 0
i.e. ( x + 3 ) ( 2x + 3 ) = 0
i.e. x + 3 = 0 or 2x + 3 = 0
x = 3 or x = 3/2

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Index
4.1 Theorem
4.2 Definition
4.3 Methods of Solving Quadratic Equations
Chapter 5
