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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,
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Posted 10 years ago
 Good point! I should have asked what has been tried... I usually do ;-)
Posted 10 years ago
 I will point out that this site is not intended for "How do I do my homework problem?" questions.
Posted 10 years ago
 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) 
Anonymous User
Anonymous User
Posted 10 years ago
 Thanks David