2019 AMC 8 Problems/Problem 20
Contents
- 1 Problem 20
- 2 Solution 1
- 3 Solution 2
- 4 Solution 3
- 5 Video Solution by Math-X (First understand the problem!!!)
- 6 Solution 3
- 7 Solution 4
- 8 Solution 5 (video of Solution 1)
- 9 Video Solution 1 (Gateway to Harder Questions)
- 10 Video Solution
- 11 Video Solution
- 12 Video Solution
- 13 Video Solution by The Power of Logic(Problem 1 to 25 Full Solution)
- 14 Video Solution by SpreadTheMathLove
- 15 See Also
Problem 20
How many different real numbers satisfy the equation
Solution 1
We have that if and only if . If , then , giving 2 solutions. If , then , giving 2 more solutions. All four of these solutions work, so the answer is . Further, the equation is a quartic in , so by the Fundamental Theorem of Algebra, there can be at most four real solutions.
Solution 2
We can expand to get , so now our equation is . Subtracting from both sides gives us . Now, we can factor the left hand side to get . If and/or equals , then the whole left side will equal . Since the solutions can be both positive and negative, we have solutions: (we can find these solutions by setting and equal to and solving for ). So, the answer is .
~UnstoppableGoddess
Solution 3
Subtract 16 from both sides and factor using difference of squares:
Quite obviously, this equation has solutions.
~TaeKim
Video Solution by Math-X (First understand the problem!!!)
https://youtu.be/IgpayYB48C4?si=EHbnc8zZoQ15Gfv6&t=6050
~Math-X
Solution 3
Associated Video - https://www.youtube.com/watch?v=Q5yfodutpsw
Solution 4
https://youtu.be/5BXh0JY4klM (Uses a difference of squares & factoring method, different from above solutions)
Solution 5 (video of Solution 1)
https://www.youtube.com/watch?v=44vrsk_CbF8&list=PLLCzevlMcsWNBsdpItBT4r7Pa8cZb6Viu&index=2 ~ MathEx
Video Solution 1 (Gateway to Harder Questions)
https://www.youtube.com/watch?v=J-E4SGEi3QE&t=2s
Video Solution
-Happytwin
Video Solution
Solution detailing how to solve the problem: https://youtu.be/x4cF3o3Fzj8
Video Solution
~Education, the Study of Everything
Video Solution by The Power of Logic(Problem 1 to 25 Full Solution)
~Hayabusa1
Video Solution by SpreadTheMathLove
https://www.youtube.com/watch?v=TpsuRedYOiM&t=250s
See Also
2019 AMC 8 (Problems • Answer Key • Resources) | ||
Preceded by Problem 19 |
Followed by Problem 21 | |
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 AJHSME/AMC 8 Problems and Solutions |
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.