Question 197201: I'm not sure if this is the right category, but I'd really appreciate your help on this multiple choice question: " If 2+i and 2-i are the roots of the equation x^2 -4x +c= 0, what is the value of c?"
a) -5 b) 5 c) -4 d)4
Thanks!
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! If 2+i and 2-i are the roots of the equation x^2 -4x +c= 0, what is the value of c?"
a) -5 b) 5 c) -4 d)4
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If those are the roots then (x-(2-i))(x-(2+i)) must divide x^2-4x+c
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But that product is ((x-2)+i)((x-2)-i) = (x-2)^2+1 = x^2-4x+4+1
= x^2 -4x + 5
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So c = 5
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Cheers,
Stan H.
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