How do you show that in the quadratic function: ax^2 + bx + c with 2 roots x1 and x2 that: 1) x1 + x2 = -b/a and 2) x1*x2 = c/a ?
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Originally Posted by JQ2009 How do you show that in the quadratic function: ax^2 + bx + c with 2 roots x1 and x2 that: 1) x1 + x2 = -b/a and 2) x1*x2 = c/a ? Use the fact that . What happens when you add up the two possible answers?
Originally Posted by JQ2009 Let and Then calculate Alternatively: Spoiler: If and are the roots of the equation , then the equation must be of the form for some constant . Therefore, we have: Equating the coefficients of x gives: But , so: Originally Posted by JQ2009 Let and Then calculate Alternatively: Spoiler: If and are the roots of the equation , then the equation must be of the form for some constant . Therefore, we have: Equating the constants gives: But , so:
then you can plug in the values for a, b and c
Last edited by sammy28; Nov 2nd 2009 at 09:51 AM. Reason: bad sign
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