PS question

[magical cook]

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


For some reason I got E but answer is D.... Can anyon confirm?

[camitava]

magical cook, OA is correct one and it should be D. Because,
f(t) = t^1/2 - 10 = s
or t^1/2 = s + 10
so t = (s + 10) ^ 2
So here comes D.

[magical cook]

Thank you,

I thin I mislead the question as square root for both x+10 instead of only x