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# Trig solutions question watch

1. So there's this question I'm confused on one bit about. Here's the whole question and solution Edexcel has:

I understand how to get the tan x = +/- √2, but then I see that they only went for the +√2. Why not -√2 too?

And why are they including the fourth quadrant too? If tan is positive in only the first and third wouldn't the solutions be: -125.3 and 54.7? Why a -54.7?
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2. (Original post by кяя)
So there's this question I'm confused on one bit about. Here's the whole question and solution Edexcel has:

I understand how to get the tan x = +/- √2, but then I see that they only went for the +√2. Why not -√2 too?

And why are they including the fourth quadrant too? If tan is positive in only the first and third wouldn't the solutions be: -125.3 and 54.7? Why a -54.7?
I don't think they did "only go for +root(2)"! I think they've solved for the case of +root(2) and then used the fact that tan(-x) = -tan x to get other possible solutions. -54.7 is allowed because it is within the allowed range of angles given, but +125.3 is NOT allowed because it lies in the 2nd quadrant.
3. (Original post by davros)
I don't think they did "only go for +root(2)"! I think they've solved for the case of +root(2) and then used the fact that tan(-x) = -tan x to get other possible solutions. -54.7 is allowed because it is within the allowed range of angles given, but +125.3 is NOT allowed because it lies in the 2nd quadrant.
Alright, thanks! They usually specify if they do the -ve too so I was confused. If that's the case I understand now

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