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November 03, 2025, 07:15:48 am
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Author Topic: Forgotten basic methods!  (Read 1386 times)  Share 

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Studyinghard

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Forgotten basic methods!
« on: March 26, 2011, 12:18:51 pm »
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Solve |sin(x/3)| = 1/2

Completely blanked on the general formula for solving this :S
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pi

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Re: Forgotten basic methods!
« Reply #1 on: March 26, 2011, 12:42:00 pm »
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I hope thats right (there are infinite solutions as you didn't specify a domain, but just add or subtract , as shown), I too haven't used the general formula for ages
« Last Edit: March 26, 2011, 01:09:20 pm by Rohitpi »
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Studyinghard

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Re: Forgotten basic methods!
« Reply #2 on: March 26, 2011, 12:58:47 pm »
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dont you have to add or subtract the period in the end, and the period is 6pi
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pi

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Re: Forgotten basic methods!
« Reply #3 on: March 26, 2011, 01:03:52 pm »
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Quote from: Studyinghard on March 26, 2011, 12:58:47 pm
dont you have to add or subtract the period in the end, and the period is 6pi

oops, knew I was forgetting something. Fixed
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taiga

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Re: Forgotten basic methods!
« Reply #4 on: March 26, 2011, 01:06:47 pm »
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ENG 1090? :P

If you think about it; it pretty much means that whatever is inside the brackets has to equal 1/2 or -1/2 in order for the modulus of it to equal 1/2. Hence Sin(x/3) = 1/2 and sin(x/3) = -1/2 are our two solutions
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Studyinghard

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Re: Forgotten basic methods!
« Reply #5 on: March 26, 2011, 01:10:54 pm »
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wait what where did you get 3npi from in your edited post :S
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taiga

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Re: Forgotten basic methods!
« Reply #6 on: March 26, 2011, 01:13:26 pm »
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I think he means 2npi

[edit] - my bad didnt read his working out, skipped to final line xD
« Last Edit: March 26, 2011, 04:15:34 pm by taiga »
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pi

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Re: Forgotten basic methods!
« Reply #7 on: March 26, 2011, 01:13:33 pm »
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Quote from: Studyinghard on March 26, 2011, 01:10:54 pm
wait what where did you get 3npi from in your edited post :S

Instead of , I simplified it down to just two solutions. btw, as it a modulus, the period is actually 3pi (ie x/3 = ...+npi,   x = ...+n3pi), not 6pi
« Last Edit: March 26, 2011, 01:28:08 pm by Rohitpi »
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Studyinghard

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Re: Forgotten basic methods!
« Reply #8 on: March 26, 2011, 03:51:34 pm »
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why is the period different for a mod function? When was this rule created :S
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pi

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Re: Forgotten basic methods!
« Reply #9 on: March 26, 2011, 03:58:05 pm »
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Quote from: Studyinghard on March 26, 2011, 03:51:34 pm
why is the period different for a mod function? When was this rule created :S


Because there are no negative ordinates (all negative ordinates turned to positive due to modulus).

The graph looks like a series of 'bumps' (ie no troughs) with a repetition (ie period) of 3pi.

Temporary image:
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Re: Forgotten basic methods!
« Reply #10 on: March 26, 2011, 04:35:30 pm »
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There's a reason why I'm so screwed for methods. -_-
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Studyinghard

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Re: Forgotten basic methods!
« Reply #11 on: April 09, 2011, 10:37:21 pm »
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BUMP. just saying that the period was wrong. it was actually 6pi
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luken93

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Re: Forgotten basic methods!
« Reply #12 on: April 10, 2011, 12:16:16 am »
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Quote from: Studyinghard on April 09, 2011, 10:37:21 pm
BUMP. just saying that the period was wrong. it was actually 6pi
I don't think it's 6pi, think about the graph, it is half of a normal sine graph...

If it were a normal sin(x/3) graph, then yes it would be 6pi, but because it is |sin(x/3)| the period is 6pi/2 = 3pi
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Studyinghard

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Re: Forgotten basic methods!
« Reply #13 on: April 10, 2011, 08:20:29 am »
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Well this was for an assignment and i got it marked wrong. Can we get more confirmations for this so I can argue this ?
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TrueTears

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Re: Forgotten basic methods!
« Reply #14 on: April 10, 2011, 05:16:57 pm »
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is the period.
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