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# This is one of my first posts on the board and came up with

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Manager
Joined: 20 Nov 2005
Posts: 55
Location: Indianapolis, IN
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This is one of my first posts on the board and came up with [#permalink]  28 Nov 2005, 18:27
This is one of my first posts on the board and came up with this question while studying (albeit while trying to watch my COLTS play the Steelers in Monday night football!!)

Problem Solving question #55 in the OG 11th ed. is a minimizing question and the explanation in the OG doesn't explain it very well for me. Isn't there some rule for easily calculating the value of X that minimizes or maximizes a given formula or am I thinking of something else?

How do I go about handling these questions?

Thanks!
Director
Joined: 14 Sep 2005
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Location: South Korea
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Re: Minimizing or maximizing a formula? [#permalink]  28 Nov 2005, 18:31
This is one of my first posts on the board and came up with this question while studying (albeit while trying to watch my COLTS play the Steelers in Monday night football!!)

Problem Solving question #55 in the OG 11th ed. is a minimizing question and the explanation in the OG doesn't explain it very well for me. Isn't there some rule for easily calculating the value of X that minimizes or maximizes a given formula or am I thinking of something else?

How do I go about handling these questions?

Thanks!

Please let me know what question it is.
_________________

Auge um Auge, Zahn um Zahn !

GMAT Club Legend
Joined: 07 Jul 2004
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Location: Singapore
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Do post the question, as not everybody owns a copy of the 11th Ed. OG. This way, more people can answer your question.

Thanks !
Manager
Joined: 20 Nov 2005
Posts: 55
Location: Indianapolis, IN
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Kudos [?]: 1 [0], given: 0

I think this one is a fairly simple one, but i feel like there must be an easy rule to remember as problems get increasingly difficult...

If y = 4 + (x - 3)^2, then y is lowest when x =
a - 14
b - 13
c - 0
d - 3
e - 4
SVP
Joined: 24 Sep 2005
Posts: 1895
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I think this one is a fairly simple one, but i feel like there must be an easy rule to remember as problems get increasingly difficult...

If y = 4 + (x - 3)^2, then y is lowest when x =
a - 14
b - 13
c - 0
d - 3
e - 4

the rule is to spread the condensed expression into the form of a quadratic expression IN CASE it's originally in condensed form
For example: y=ax^2+bx+c . This is a parabola. The biggest/ smallest of y then is the peak/ nadir of the parabola. The formula for this point is :
-( b^2-4ac)/ (-4a) ( if i remember correctly, i'll double-check it)

1) if the expression contains -x^2, the question asks for the peak/ the biggest value.
2) if the expression contains x^2, the question asks for the nadir/ the smallest value.

For example: y=x^2 - 6x + 12
the nadir is -[((-6)^2- 4*12*1)/ 4*1] = 3 --> the smallest value of y is 3

OR you can solve it another way by trying to group the expression into froms of - (ax+b)^2 +c OR (ax+b)^2 +c
For example: x^2-6x+12= (x-3)^2+3
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