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How would you show this?

Anonymous User
Anonymous User
Posted 10 years ago

Suppose that x1 and x2 are the roots of the quadratic equation ax^2+bx+c By writing this in the form

a(x-x1)(x-x2)=0 

Show that

x1x2=c/a
x1+x2=-b/a 

Hence write down a quadratic equation with roots 3+2i and 1-i,

POSTED BY: Anonymous User
4 Replies

Good point! I should have asked what has been tried... I usually do ;-)

POSTED BY: David Reiss

I will point out that this site is not intended for "How do I do my homework problem?" questions.

POSTED BY: Daniel Lichtblau
In[6]:= solution = Solve[a x^2 + b x + c == 0, x]

Out[6]= {{x -> (-b - Sqrt[b^2 - 4 a c])/(
   2 a)}, {x -> (-b + Sqrt[b^2 - 4 a c])/(2 a)}}

In[7]:= {x1, x2} = x /. solution

Out[7]= {(-b - Sqrt[b^2 - 4 a c])/(2 a), (-b + Sqrt[b^2 - 4 a c])/(
 2 a)}

In[8]:= x1 x2 // Simplify

Out[8]= c/a

In[9]:= x1 + x2 // Simplify

Out[9]= -(b/a)
POSTED BY: David Reiss
Anonymous User
Anonymous User
Posted 10 years ago

Thanks David

POSTED BY: Anonymous User
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