Question 153051
Example:
If a = 1
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x^2 + 5x + 6
The procedure is called "the AC Method".
1st: think of two numbers whose product is AC = 1*6 = 6
and whose sum is B = 5
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The numbers are 2 and 3
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2nd: Replace the B-term by the sum you have found:
x^2 _+ 2x + 3x + 6
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3rd: Factor and 1st two and the last two terms separately:
x(x+2) + 3(x+2)
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4th: Factor again to get the answer:
(x+2)(x+3
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Example: 
a not equal to 1
2x^2 - x - 21
1st: think of two numbers whose product is AC = 2*21 = 42
and whose sum is B = -1
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The numbers are -7 and 6
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2nd: replace the B-term with the sum you found:
2x^2 -7x+6x -21
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3rd: factor the 1st two and the last two terms separately:
x(2x-7) +3(2x-7)
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4th: Facor again
(2x-7)(x+3)
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Cheers,
Stan H.