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by jayanti » Fri Aug 05, 2011 4:22 am
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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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by knight247 » 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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by gmatboost » 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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by MBA.Aspirant » Sat Aug 06, 2011 3:26 pm
u = f(t) = √t - 10

(u+10)^2 = t
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by [email protected] » Sat Apr 07, 2018 2:17 pm
Hi All,

We're told that the function f is defined by f(X) = (√X) - 10 for all positive numbers X and that U = f(T) for some positive numbers T and U. We're asked for T in terms of U. While this question might look 'scary', you can solve it by doing some basic work on your pad and TESTing VALUES.

To start, 'function questions' are essentially just about plugging in a value and determining the result (similar to graphing an individual points of an equation in co-ordinate Geometry).

We're told that U = f(T), so we'll pick a value for T, plug it into the given function and the result with be the value of U.

IF.....
T=4, then f(4) = (√4) - 10 = 2 - 10 = -8
U = -8

We're asked for T in terms of U, so we're looking for an answer that equals 4 when we plug in U = -8. There's only one answer that matches...

Final Answer: D

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