Difference between revisions of "2002 AMC 12P Problems/Problem 17"

(Problem)
(Problem)
Line 1: Line 1:
 
== Problem ==
 
== Problem ==
If <math>a,b,c</math> are real numbers such that <math>a^2 + 2b =7</math>, <math>b^2 + 4c= -7,</math> and <math>c^2 + 6a= -14</math>, find <math>a^2 + b^2 + c^2.</math>
+
Let <math>f(x) = \sqrt{\sin^4{x} + 4 \cos^2{x}} - \sqrt{\cos^4{x} + 4 \sin^2{x}}.</math> An equivalent form of <math>f(x)</math> is
  
 
<math>
 
<math>
\text{(A) }14
+
\text{(A) }1-\sqrt{2}\sin{x}
 
\qquad
 
\qquad
\text{(B) }21
+
\text{(B) }-1+\sqrt{2}\cos{x}
 
\qquad
 
\qquad
\text{(C) }28
+
\text{(C) }\cos{\frac{x}{2}} - \sin{\frac{x}{2}}
 
\qquad
 
\qquad
\text{(D) }35
+
\text{(D) }\cos{x} - \sin{x}
 
\qquad
 
\qquad
\text{(E) }49
+
\text{(E) }\cos{2x}
 
</math>
 
</math>
 +
 +
[[2002 AMC 12P Problems/Problem 17|Solution]]
  
 
== Solution ==
 
== Solution ==

Revision as of 23:53, 29 December 2023

Problem

Let $f(x) = \sqrt{\sin^4{x} + 4 \cos^2{x}} - \sqrt{\cos^4{x} + 4 \sin^2{x}}.$ An equivalent form of $f(x)$ is

$\text{(A) }1-\sqrt{2}\sin{x} \qquad \text{(B) }-1+\sqrt{2}\cos{x} \qquad \text{(C) }\cos{\frac{x}{2}} - \sin{\frac{x}{2}} \qquad \text{(D) }\cos{x} - \sin{x} \qquad \text{(E) }\cos{2x}$

Solution

Solution

If $\log_{b} 729 = n$, then $b^n = 729$. Since $729 = 3^6$, $b$ must be $3$ to some factor of 6. Thus, there are four (3, 9, 27, 729) possible values of $b \Longrightarrow \boxed{\mathrm{E}}$.

See also

2002 AMC 12P (ProblemsAnswer KeyResources)
Preceded by
Problem 16
Followed by
Problem 18
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 12 Problems and Solutions

The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions. AMC logo.png