Absolutely Absolute Absolutness

Algebra Level 5

How many solutions does the equation below have?

x 8 10 4 5 1 = 0 \Huge| \huge| \Large| \large||x-8| -10|- 4\Large| \large-5 \huge| \large-1 \Huge| \large{=0}


The answer is 9.

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2 solutions

Shourya Pandey
Jun 26, 2017

x 8 10 4 5 1 = 0 \displaystyle |||||x-8| - 10| - 4| - 5 | - 1| = 0

x 8 10 4 5 = 1 \displaystyle \iff ||||x-8| - 10| - 4| - 5 | = 1

x 8 10 4 = 6 or 4 \displaystyle \iff |||x-8| - 10| - 4| = 6 \text{ or } 4

x 8 10 = 2 , 10 , 0 or 8 \displaystyle \iff ||x-8| - 10| = -2 , 10 , 0 \text{ or } 8 , but 2 -2 is discarded , obviously

x 8 = 0 , 20 , 10 , 2 or 18 \displaystyle \iff |x-8| = 0, 20 , 10 , 2 \text{ or } 18

x = 8 , 12 , 28 , 2 , 18 , 6 , 10 , 10 or 26 \displaystyle \iff x = 8 , -12 , 28 , -2 , 18 , 6 , 10 , -10 \text{ or } 26 , i.e., there are 9 9 possible values of x x .

Nice and simple! :)

Michael Huang - 3 years, 11 months ago
Marta Reece
Jun 26, 2017

x 8 10 \large||x-8| -10| with y = 4 y=4 marked in yellow.

x 8 10 4 \Large| \large||x-8| -10|- 4\Large| with y = 5 y=5 in yellow.

x 8 10 4 5 \huge| \Large| \large||x-8| -10|- 4\Large| \large-5 \huge| with y = 1 y=1 in yellow.

x 8 10 4 5 1 \Huge| \huge| \Large| \large||x-8| -10|- 4\Large| \large-5 \huge| \large-1 \Huge|

How are all the graphs plotted? Must we resort to computers to get the answer?

Pi Han Goh - 3 years, 11 months ago

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The reason I used drawings was to show the behavior of the function. The plots were done using Microsoft Word, painstakingly and without math software of any kind.

Marta Reece - 3 years, 11 months ago

The solution method itself could have been done with graph paper, no need for computer.

Wesley Zumino - 3 years, 10 months ago

Do you mean " y =4 marked in yellow", " y =5 marked in yellow", and " y =1 marked in yellow" ?

Geoff Pilling - 3 years, 11 months ago

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Yes, I am on my way out the door going on a full night search and rescue mission, way too much to think about.

Marta Reece - 3 years, 11 months ago

@Marta Reece - Interesting to see a graphical view of a solution, gives me a different perspective on it. My solution was exactly that of @Shourya Pandey , i.e., purely algebraic. Thanks for taking the time to do the graphics. I appreciate how much effort it takes.

Wesley Zumino - 3 years, 10 months ago

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Thank you. I tend to do my solving of many problems visually, and frequently find it difficult to explain to others. I am glad to hear when I have succeeded. Thanks again.

Marta Reece - 3 years, 10 months ago

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