Difference between revisions of "2002 AMC 10P Problems/Problem 12"

(Solution 1)
(Solution 1)
Line 35: Line 35:
 
= a^{336}  
 
= a^{336}  
 
\neq a^{2002}</math>
 
\neq a^{2002}</math>
 +
 +
<math>\text{II. } f_{11}(a)f_{13}(a)f_{14}(a)</math>
 +
 +
<math>f_{11}(a)f_{13}(a)f_{14}(a)
 +
=a^{11}a^{13}a^{14}
 +
=a^{38}
 +
\neq a^{2002}</math>
 +
 +
<math>\text{III. } (f_{11}(f_{13}(a)))^{14}</math>
 +
 +
<math>(f_{11}(f_{13}(a)))^{14}
 +
=((a^{13})^{11})^{14}
 +
=a^{13 \cdot 11 \cdot 14}
 +
=a^{2002}</math>
 +
 +
<math>\text{IV. } f_{11}(f_{13}(f_{14}(a)))</math>
 +
 +
<math>f_{11}(f_{13}(f_{14}(a)))
 +
=((a^{14})^{13})^{11}
 +
=a^{14 \cdot 13 \cdot 11}
 +
=a^{2002}</math>
 +
 +
Thus, our answer is <math>\text{(C) III and IV only}.</math>
  
 
== See also ==
 
== See also ==
 
{{AMC10 box|year=2002|ab=P|num-b=11|num-a=13}}
 
{{AMC10 box|year=2002|ab=P|num-b=11|num-a=13}}
 
{{MAA Notice}}
 
{{MAA Notice}}

Revision as of 05:52, 15 July 2024

Problem 12

For $f_n(x)=x^n$ and $a \neq 1$ consider

$\text{I. } (f_{11}(a)f_{13}(a))^{14}$

$\text{II. } f_{11}(a)f_{13}(a)f_{14}(a)$

$\text{III. } (f_{11}(f_{13}(a)))^{14}$

$\text{IV. } f_{11}(f_{13}(f_{14}(a)))$

Which of these equal $f_{2002}(a)?$

$\text{(A) I and II only} \qquad \text{(B) II and III only} \qquad \text{(C) III and IV only} \qquad \text{(D) II, III, and IV only} \qquad \text{(E) all of them}$

Solution 1

We can solve this problem with a case by case check of $\text{I., II., III.,}$ and $\text{IV.}$ Since $f_n=x^n,$ $f_{2002}(a)=a^{2002},$ all cases must equal $a^{2002}.$

$\text{I. } (f_{11}(a)f_{13}(a))^{14}$

$(f_{11}(a)f_{13}(a))^{14}  =(a^{11}a^{13})^{14}  = (a^{24})^14  = a^{336}  \neq a^{2002}$

$\text{II. } f_{11}(a)f_{13}(a)f_{14}(a)$

$f_{11}(a)f_{13}(a)f_{14}(a) =a^{11}a^{13}a^{14} =a^{38} \neq a^{2002}$

$\text{III. } (f_{11}(f_{13}(a)))^{14}$

$(f_{11}(f_{13}(a)))^{14} =((a^{13})^{11})^{14} =a^{13 \cdot 11 \cdot 14} =a^{2002}$

$\text{IV. } f_{11}(f_{13}(f_{14}(a)))$

$f_{11}(f_{13}(f_{14}(a))) =((a^{14})^{13})^{11} =a^{14 \cdot 13 \cdot 11} =a^{2002}$

Thus, our answer is $\text{(C) III and IV only}.$

See also

2002 AMC 10P (ProblemsAnswer KeyResources)
Preceded by
Problem 11
Followed by
Problem 13
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
All AMC 10 Problems and Solutions

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