Abhimanyu111
Which if the following has a root in common with x^2 - 6x + 5 = 0
A. x^2+ 1 = 0
B. x^2 - x-2 = 0
C. x^2 - 10x - 5 = 0
D. 2x^2 - 2 = 0
E. x^2 - 2x-3 = 0
Factor the quadratic to find its roots
\(x^2 - 6x + 5 = 0\)
\((x - 1)(x - 5)= 0\)
\(x = 1\) or \(x = 5\)
Plug both roots into the answer choices. Scan the choices first.
Eliminate A (inevitable positive result, not 0); and
Eliminate C (with roots this small, inevitable negative result).*
FillFM 's link** and
GMATPrepNow 's article are helpful. +1
The arithmetic here is easy. I started with B. This question took a little over half a minute.
Analysis of all choices for those who are curious:
A. \(x^2+ 1 = 0\)
\(x=1\): \((1+1) = 2\) NO
\(x=5\): \((25+1)=26\) NO
B. \(x^2 - x-2 = 0\)
\(x=1\): \((1-1-2) = -2\) NO
\(x=5\): \((25-5-2) = 18\) NO
C. \(x^2 - 10x - 5 = 0\)
\(x=1\): \((1-10-5) = -14\)
\(x=5\): \((25-50-5) = -30\)
D. \(2x^2 - 2 = 0\)
\(x=1\): \((2-2) = 0\) YES
Finished. We just need one root.
In case there is doubt, (D) cont.:
\(x=5\): \((50-2=48)\) NO. Does not matter. We need
"a" root (one) in common. We have \(x = 1\)
E. \(x^2 - 2x-3 = 0\)
\(x=1\): \((1-2-3) = -4\)
\(x=5\): \((25-10-3) = 12\) NO
ANSWER D
*Eliminate A: Both roots are positive. Answer A has two positive terms and a plus sign. Positive roots cannot make that equation true.
Eliminate C: For roots 1 and 5, the squared \(a\) term is not great enough to overcome the negative coefficient of the \(b\) term
** FillFM links to an excellent article that recommends starting with E for "analyze the answer choices". (The stats are startling.) I'm a bit paranoid. GMAC adapts to public warnings.