Questions on Algebra: Linear Algebra (NOT Linear Equations) answered by real tutors!

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Question 166538: What is the sum of the roots of the equation
ax^2+bx+c=0
: What is the sum of the roots of the equation
ax^2+bx+c=0

Answer by jim_thompson5910(9924) About Me  (Show Source):
You can put this solution on YOUR website!
Remember the quadratic formula is:


x = (-b +- sqrt( b^2-4ac ))/(2a) note: a<>0


Now let w=sqrt( b^2-4ac ) (to simplify things a bit)


So the quadratic formula becomes


x = (-b +- w)/(2a)


which really breaks down to


x = (-b + w)/(2a) or x = (-b - w)/(2a)


So the first root is x[1] = (-b + w)/(2a) and the second root is x[2] = (-b - w)/(2a)


==========================================

Adding the Roots:



x[1]+x[2] Now let's add the roots


(-b + w)/(2a)+(-b - w)/(2a) Plug in x[1] = (-b + w)/(2a) and x[2] = (-b - w)/(2a)


(-b + w-b - w)/(2a) Combine the fractions.


((-b-b) + (w-w))/(2a) Group like terms.


(-2b)/(2a) Combine like terms. Notice how the "w" terms cancel each other out completely.


-b/a Reduce


So this shows us that the sum of the roots of ax^2+bx+c is -b/a

Question 166538: What is the sum of the roots of the equation
ax^2+bx+c=0
: What is the sum of the roots of the equation
ax^2+bx+c=0

Answer by stanbon(19742) About Me  (Show Source):
You can put this solution on YOUR website!
What is the sum of the roots of the equation
ax^2+bx+c=0
Roots: x = [-b + sqrt(b^2-4ac)]2a or x = [-b -sqrt(b^2-4ac)]/2a
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Adding you get [-b/2a] + [-b/2a]
= 2[-b/2a]
= -b/a
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Cheers,
Stan H.