Damazo T. answered • 09/29/14
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Hello, Tiff
The first thing that I am going to do is rewrite the problem
x^2-9x+20= 0 I just added 20 to both sides
(x-4) (x-5)=0
x^2+bx+c= 0 The is the form that this problem is written. In this problem, b=-9, c=20.
If you are wondering why it is (x-5)(x-4). I will try to explain this to you as succinctly as possible.
The first thing you must do is find the factors of 20: 1,-1,2,-2,4,-4, 5, -5, 10, -10, 20, -20. Now, you need to find two factors of 20 that add up to -9 and when you multiply the give you a 20. Let just try a couple.
a) -10, 1: add up to -9, but their product is not 20.
b) -4, -5: add up to -9 and the product is 20. This pair woks
I hope this helps out. With a little practice, you will become an expert in no time. Thanks for posting.
D. Y. T.
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