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Mathematics 21 Online
OpenStudy (anonymous):

whats 3|3k|=27 ?

jimthompson5910 (jim_thompson5910):

First we must divide both sides by 3 3|3k| = 27 |3k| = 27/3 |3k| = 9

jimthompson5910 (jim_thompson5910):

Then we use the idea that if |x| = p, then x = p or x = -p to go from this equation |3k| = 9 to these two equations 3k = 9 or 3k = -9

jimthompson5910 (jim_thompson5910):

solve those last two equations to get your two answers

OpenStudy (anonymous):

9

jimthompson5910 (jim_thompson5910):

3k = 9, so k = ??

jimthompson5910 (jim_thompson5910):

3k means "3 times k"

OpenStudy (tkhunny):

\(3|3k| = 27\) Divide by 3 \(|3k| = 9\) Figure out that 3 is positive and the absolute values do nothing \(3|k| = 9\) Divide by 3 \(|k| = 3\) Easier yet?

OpenStudy (anonymous):

how do you get 27

OpenStudy (tkhunny):

?? From the problem statement?

OpenStudy (tkhunny):

Do you mean to say some answer key says a solution is k = 27? That would be incorrect.

OpenStudy (anonymous):

yea.

OpenStudy (tkhunny):

AS WRITTEN, we have k = 3 or k = -3.

jimthompson5910 (jim_thompson5910):

think of 3k = 9 as a statement saying "3 times _____ equals 9" what goes in the blank?

OpenStudy (anonymous):

k ?

jimthompson5910 (jim_thompson5910):

yes, but what number also goes in the blank in place of k?

jimthompson5910 (jim_thompson5910):

3 times SOME NUMBER equals 9 what replaces "SOME NUMBER" ?

OpenStudy (anonymous):

- 3 ?

jimthompson5910 (jim_thompson5910):

why is it negative?

jimthompson5910 (jim_thompson5910):

3 times -3 is positive 9 ? that's a true statement?

OpenStudy (anonymous):

no ?

jimthompson5910 (jim_thompson5910):

it's not

jimthompson5910 (jim_thompson5910):

it should be 3 times 3 = 9

jimthompson5910 (jim_thompson5910):

so the solution to 3k = 9 is k = 3

jimthompson5910 (jim_thompson5910):

in a very similar fashion, the solution to 3k = -9 is k = -3

jimthompson5910 (jim_thompson5910):

Another way to see that k = 3 is the solution to 3k = 9 is to divide both sides of 3k = 9 by 3 to isolate k

OpenStudy (anonymous):

\[{-3 , 9 }\] ?

jimthompson5910 (jim_thompson5910):

I don't know what you mean there. Are you saying the two answers are k = -3 and k = 9 ?

OpenStudy (anonymous):

yea.

jimthompson5910 (jim_thompson5910):

that's not correct

jimthompson5910 (jim_thompson5910):

how did you get k = 9?

OpenStudy (anonymous):

study guide , help

jimthompson5910 (jim_thompson5910):

do you see how I got 3k = 9 and 3k = -9 ?

OpenStudy (anonymous):

no , i really suck at math

jimthompson5910 (jim_thompson5910):

go back to my steps and tell me where you got stuck

OpenStudy (anonymous):

Then we use the idea that if |x| = p, then x = p or x = -p to go from this equation |3k| = 9 to these two equations 3k = 9 or 3k = -9

OpenStudy (anonymous):

that part

jimthompson5910 (jim_thompson5910):

that rule allows us to say things like |x| = 7 turns into x = 7 or x = -7

jimthompson5910 (jim_thompson5910):

or if |x| = 3, then x = 3 or x = -3

jimthompson5910 (jim_thompson5910):

|x| = 3 means that some number x is 3 units away from zero The numbers 3 and -3 are both 3 units away from zero, which is why the two answers to |x| = 3 are x = 3 or x = -3

jimthompson5910 (jim_thompson5910):

so if I had |x| = 5, then what are the two solutions to x?

OpenStudy (anonymous):

|x| = 5 or |x| = -5 ?

jimthompson5910 (jim_thompson5910):

no, it should be x = 5 or x = -5 those two numbers are five units away from zero (on the number line)

jimthompson5910 (jim_thompson5910):

absolute value is basically "distance the number is from zero on the number line"

jimthompson5910 (jim_thompson5910):

what about something like |x| = 14 what are the two solutions to x?

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