SOLUTION: Hi How do I solve this problem by Completing the Square? IS it similar to the Quadratic Formula? SOLVE: {{{3x^2-9x-12=0}}} Thank you so much ! I do greatly appreciate it

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: Hi How do I solve this problem by Completing the Square? IS it similar to the Quadratic Formula? SOLVE: {{{3x^2-9x-12=0}}} Thank you so much ! I do greatly appreciate it      Log On


   

Question 1041956: Hi
How do I solve this problem by Completing the Square?
IS it similar to the Quadratic Formula?
SOLVE:
3x%5E2-9x-12=0
Thank you so much ! I do greatly appreciate it !!!
Found 2 solutions by Alan3354, Koala:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
3x%5E2-9x-12=0
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Divide by 3
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x%5E2+-+3x+-+4+=+0
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x%5E2+-+3x+=+4
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Add (b/2a)^2 to each side
x%5E2+-+3x+%2B+9%2F4=+4+=+9%2F4+=+25%2F4
%28x+-+3%2F2%29%5E2+=+25%2F4
Can you finish?

Answer by Koala(6) About Me  (Show Source):
You can put this solution on YOUR website!
3x^2-9x = 12; Divide all terms by 3; x^2-3x = 4; Add (b/2)^2 (where b is equal to -3) to both sides; x^2-3x+(9/4) = 4+(9/4); Simplify; [x-(3/2)]^2 = 25/4; Take the square root of both sides; x-(3/2) = 5/2; x = 5/2 + 3/2 = 4 ; And; x-(3/2) = -5/2; x = -5/2 + 3/2;x = -1; So the answers are {x = 4 & x = -1}. It is not similar to quadratic formula because in quadratic formula, you will just substitute the values of a, b, and c; while in completing the square, you will add (b/2)^2 to both sides and take the square root of the both sides to find the values of x.