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# Trigonometry question watch

1. Hi!

I'm re-doing some trigonometry basics in my spare time with a few A-level textbooks because I want to do some more studying in the future. Occasionally running into a few simple things I can't remember the explaination for. In this trig equation question:

4sinx=3tanx, -180<x<180 which I rearrange to give cosx=3/4.

I get the answers (+/-)41.41 degrees and 0 which are correct, but the textbook answer section also lists (+/-)180 degrees as an answer! I thought that the only way (+/-)180 would be an answer is if cosx had a negative value but I've run into this a few times and think I must have just forgotten why it happens.

2. (Original post by SGR2917)
Hi!

I'm re-doing some trigonometry basics in my spare time with a few A-level textbooks because I want to do some more studying in the future. Occasionally running into a few simple things I can't remember the explaination for. In this trig equation question:

4sinx=3tanx, -180<x<180 which I rearrange to give cosx=3/4.

I get the answers (+/-)41.41 degrees and 0 which are correct, but the textbook answer section also lists (+/-)180 degrees as an answer! I thought that the only way (+/-)180 would be an answer is if cosx had a negative value but I've run into this a few times and think I must have just forgotten why it happens.

You lost this solution because you cancelled sin(x) off both sides, instead of factoring it out.
latex in progress...
, so or .
done
3. (Original post by EricPiphany)
You lost this solution because you cancelled sin(x) off both sides, instead of factoring it out.
latex in progress...
, so or .
done
That makes complete sense. Much appreciated! Thanks

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