If function f(x) = x² + 2bx + 4, then for any b, f(x) is the least whe

Hi Bunuel !!!!!

We can use differentiation approach too....I know this is out of scope but still we are bothered about getting right answer in least possible time....put df(x)/d(x) = 0.....d(x^2 + 2bx + 4)/d(x)=0....i.e. 2x + 2b = 0.......x=-b

Hi All,

This question can be solved by TESTing VALUES.

We're given the function f(X) = X^2 + 2BX + 4. We're told for ANY value of B, f(X) is LEAST when X = what value.

This means that we can choose ANY value we want for B and the answer will stay the SAME. Looking at the 5 answer choices, I don't want to use B=0 or B=2 (since those two possibilities would create duplicate answers); so I'll use...

B = 1

f(X) = X^2 + 2X + 4

Which of the following answers gives us the LEAST result when X = ......

A: X = -1 --> -1 - \sqrt{-3} = nonsenscial answer. Eliminate A.

B: X = -2 --> 4 - 4 + 4 = 4

C: X = 0 --> 0 + 0 + 4 = 4

D: X = -1 --> 1 - 2 + 4 = 3

E: X = -3 --> 9 - 6 + 4 = 7

Final Answer:

GMAT assassins aren't born, they're made,
Rich

SEEMS TO BE THE BEST APPROACH.

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