S Smilebuffalo Member Joined Jun 9, 2008 Messages 89 Location Fairfield West Gender Male HSC 2010 Mar 14, 2010 #1 If ax^3 + cx + d = 0 has a double root, show that 27ad^2 + 4c^3 = 0
B bleaver New Member Joined Apr 19, 2009 Messages 14 Gender Male HSC 2010 Mar 14, 2010 #2 We can then substitute this root into the original equation. I've skipped a few lines of simplification but work thruogh it and it should be obvious.
We can then substitute this root into the original equation. I've skipped a few lines of simplification but work thruogh it and it should be obvious.
S Smilebuffalo Member Joined Jun 9, 2008 Messages 89 Location Fairfield West Gender Male HSC 2010 Mar 14, 2010 #3 how come when you rooted it, you ignored the negative root?
B bleaver New Member Joined Apr 19, 2009 Messages 14 Gender Male HSC 2010 Mar 14, 2010 #4 Think about it. If I put the negative root as a possibility, once I square both sides, that negative is gone leaving you with the same result as the positive possibility.
Think about it. If I put the negative root as a possibility, once I square both sides, that negative is gone leaving you with the same result as the positive possibility.
