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Functions

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jayanti Senior | Next Rank: 100 Posts
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Functions

Post Fri Aug 05, 2011 4:22 am
The function f is defined by f(x) = √x - 10 for all positive numbers x. If u = f(t) for some positive numbers t and u. What is t in terms of u?

A. √(u+10)
B. (√u + 10)^2
C. √(u^2+10)
D. (u + 10)^2
E. (u^2 + 10)^2

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MBA.Aspirant Master | Next Rank: 500 Posts Default Avatar
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Post Sat Aug 06, 2011 3:26 pm
u = f(t) = √t - 10

(u+10)^2 = t

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gmatboost Master | Next Rank: 500 Posts
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Post Fri Aug 05, 2011 10:21 am
You can also plug in for t, find u, and then check the answers.

Say, t = 9 (pick a square since we need to take the square root).
u = f(t) = √t - 10 = √9 - 10 = 3 - 10 = -7

Now you can plug in u = -7 and see which answer gives you t = 9.

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knight247 Legendary Member
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Post Fri Aug 05, 2011 4:41 am
f(x)=√x - 10
f(t)=√t - 10

Also, u=f(t)
u=√t - 10
√t=u+10
t=(u+10)^2

Hence D

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