SOLUTION: What value of b will make the expression x^2-bx+40 a perfect square?

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Question 120251: What value of b will make the expression x^2-bx+40 a perfect square?
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
What value of b will make the expression x^2-bx+40 a perfect square?
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Perfect Square form: (c-d)^2 = c^2-2cd+d^2
Your Problem:
d^2 = 40
d = 2sqrt(10)
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c^2=x^2
c=x
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-2cd=-bx
Substitute to get:
bx = 2x(2sqrt(10))
bx = 4sqrt(10)x
b = 4sqrt(10)
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Cheers,
Stan H.