Difference between revisions of "2016 AMC 12A Problems/Problem 16"
(→Solution) |
(→Solution) |
||
| Line 9: | Line 9: | ||
Setting the first two equations equal to each other, <math>\log_3 x = \log_x 3</math>. | Setting the first two equations equal to each other, <math>\log_3 x = \log_x 3</math>. | ||
| − | Solving this, we get <math>\left(3, 1\right)</math> and <math>\left( | + | Solving this, we get <math>\left(3, 1\right)</math> and <math>\left(\frac{1}{3}, -1\right)</math>. |
| − | Similarly with the last two equations, we get <math>\left(3, -1\right)</math> and <math>\left(\frac{1}{3}, | + | Similarly with the last two equations, we get <math>\left(3, -1\right)</math> and <math>\left(\frac{1}{3}, 1\right)</math>. |
Now, by setting the first and third equations equal to each other, we get <math>\left(1, 0\right)</math>. | Now, by setting the first and third equations equal to each other, we get <math>\left(1, 0\right)</math>. | ||
Revision as of 19:31, 6 February 2016
Problem 16
The graphs of 
and 
are plotted on the same set of axes. How many points in the plane with positive 
-coordinates lie on two or more of the graphs?
Solution
Setting the first two equations equal to each other, 
.
Solving this, we get 
and 
.
Similarly with the last two equations, we get 
and 
.
Now, by setting the first and third equations equal to each other, we get 
.
Pairing the first and fourth or second and third equations won't work because then 
.
Pairing the second and fourth equations will yield 
, but since you can't divide by 
, it doesn't work.
After trying all pairs, we have a total of 
solutions 
See Also
| 2016 AMC 12A (Problems • Answer Key • Resources) | |
| Preceded by Problem 15 |
Followed by Problem 17 |
| 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. 
