vinni.k wrote:Which of the following is always equal to √(9 + x^2 -6x) ?
A.x -3
B.3 + x
C.|3 - x|
D.|3 +x|
E.3 - x
OA is C
Let x=1.
In this case, √(9 + x² - 6x) = √4 = 2.
Now plug x=1 into the answer choices and eliminate any that don't yield a value of 2.
A. x -3 = 1-3 = -2.
B. 3 + x = 3 + 1 = 4.
C. |3 - x| = |3-1| = 2.
D. |3 +x| = |3+1| = 4.
E. 3 - x = 3-1 = 2.
Eliminate A, B and D.
Test an EXTREME value.
Let x=10.
In this case, √(9 + x² - 6x) = √49 = 7.
Now plug x=10 into the remaining answer choices and eliminate any that don't yield a value of 7.
C. |3 - x| = |3-10| = 7.
E. 3 - x = 3-10 = -7.
Eliminate E.
The correct answer is
C.
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