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x^2+3x-12=0

I need to factor this and thought I knew how, but I can't figure this one out. Factors of 12 are 1,12; 2,6; 3,4 and when I subtract these I don't get the 3 I need for the 3x. Am I overlooking something? My other problems were easy, so I don't think this would be a decimal or a fraction. Thank you for any help!!

User Icon for bobpursley bobpursley answered
13 years ago

lets do it by completion of the square:

x^2+3x+9/4=12+9/4
(x+3/2)^2=57/4

x=-3/2+-sqrt 14.25

so it factors, but into irrational numbers.

(x+1.5+sqrt 14.25)(x+1.5-sqrt 14.25)=0

nice, huh?