Factorising Quadratics

Highest Common Factor Method

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  • Created on: 26-09-11 13:22
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Factorising Quadratics(where last sign is a plus) Example
2
1) 4x 12x+9
Times, first number by last number 4x9= 36
Find all the pairs of factors of 36 until you find the pair that add up to
the middle number12
1x36
6x6 (6+6=12)
Prepare two brackets
( )( )
2) Compare the first number of the Quadratic equation (4x2 12x+9) with the first
number in the pair of factors (6x6) and find a factor of both numbers
A factor of 4 and 6 is 2 so therefore, 2 will be the first number in the
bracket which means we will put an X next to it
( 2x )( )
3) Compare the last number of the quadratic equation (4x2 12x+9) with the last
number of the pairs of factors (6x6) and find a factor of both numbers
A factor of 9 and 6 is 3, therefore, to complete the bracket we will put
3 next to the 2x
However to determine if the sign is + or , you would have to look at
the first sign in the quadratic equation. In this case, sign
(2x3)( )
4) Finally to finish of you need to times the 2x by ....to get 4x2, therefore the number in
the second bracket will be 2x because 2xX2x is 4x
(2x3)(2x )
To determine the number in the second bracket after the 2x, you will
need to find a number that will times 3 to give you the last number of
the quadratic which is 9. 3x3 is 9 therefore, 3 will be put next to the
2x in the second bracket
(2x3)(2x3)

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Factorising Quadratics(where last sign is a minus) Example
1) 10x2 19x2
Times, first number by last number 10x2= 20
Find all the pairs of factors of 20 until you find the pair that minus to give
the middle number19
1x20 (120= 19)
Prepare two brackets
( )( )
2) Compare the first number of the Quadratic equation (10x2 19x2) with the first
number in the pair of factors (1x20) and find a factor of both numbers
A factor of 10 and 1 is 1 so…read more

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