# SOLUTION: This is a basic question but I can seem to explain it. The Quadratic Equation term "b^2 -4ab" why do we change it to "b^2+ 4ab" when the "b" value is negative? Thanks annmrj@aol.co

Algebra ->  -> SOLUTION: This is a basic question but I can seem to explain it. The Quadratic Equation term "b^2 -4ab" why do we change it to "b^2+ 4ab" when the "b" value is negative? Thanks annmrj@aol.co      Log On

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 Question 22: This is a basic question but I can seem to explain it. The Quadratic Equation term "b^2 -4ab" why do we change it to "b^2+ 4ab" when the "b" value is negative? Thanks annmrj@aol.com EX: b^2-4ab (x^2-6x-27=0) = 6^2+4(1)(-27)=144 Answer by AnlytcPhil(1321)   (Show Source): You can put this solution on YOUR website!```This is a basic question but I can seem to explain it. The Quadratic Equation term "b^2 -4ab" why do we change it to "b^2+ 4ab" when the "b" value is negative? ---------------------------------------------------- We don't. First of all it's not b²-4ab, it's b²-4ac. Also your example: b^2-4ab (x^2-6x-27=0) = 6^2+4(1)(-27)=144 is incorrect in the next to last step, although 144 is correct. It should be b^2-4ab (x^2-6x-27=0) = 6^2-4(1)(-27)=144 What you have there, namely, 6^2+4(1)(-27)= equals to -72, not 144. Suppose we have 2x² + 5x - 3 then a=2, b=5, and c=-3 So b² - 4ac becomes (5)² - 4(2)(-3) or 25 - (-24) and then the " - " sign before the parentheses and the " - " before the 24 inside the parentheses becomes a " + ", and we have 25 + 24 or 49 Edwin ```