SOLUTION: Find the value of k so that 2x^2-kx+5=0 has one real rational root.

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Question 101757: Find the value of k so that 2x^2-kx+5=0 has one real rational root.
Answer by HyperBrain(694) About Me  (Show Source):
You can put this solution on YOUR website!
ax%5E2%2Bbx%2Bc=0 has one root if and only if b%5E2-4ac=0

Since 2x%5E2-kx%2B5=0 has one real root, then,
%28-k%29%5E2-4%2A2%2A5=0
k%5E2-40=0
k%5E2=0%2B40
k%5E2=40
k=+0%2B-sqrt%2840%29
k=0%2B-sqrt%284%2A10%29
k=0%2B-sqrt%284%29sqrt%2810%29
k=0%2B-2sqrt%2810%29

thus, k=2sqrt%2810%29 or k=-2sqrt%2810%29

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