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Points or no points

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What up guys.

Just got a question regarding the marking system for externals.

Simply, I have answered a trigo question in paper 1 that was asking for me to find "tan (2x)" with "cos (x)" given in fraction form.

Well..I used the tan (2x) formula to solve as shown here (the 3rd one) ->Image result for tan 2x formula

After answering the paper, I was checking my answers. Then I suddenly recalled "tan (2x)" formula isn't included in the SL syllabus.

The markscheme only showed using " [sin (2x)] / [cos (2x)]" to solve the question, nothing related to the 3rd formula in the shown above. In fact, it was worth 6 points if I'm not mistaken.

If ever I use the tan (2x) formula above, will I be able to receive full marks? I have already inquired this to my math teacher, he however doubt to answer as he wasn't sure.

 

Would really appreciate your help. Thanks in advance!

Edited by mrunknown

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An examiner should give you the points assuming you used the first two formulas and worked out the answer from there, regardless of whether it was in the syllabus or a simpler way was available. If IB didn't intend that, they'd outsource the work to factory workers rather than math teachers who would be able to recognize some basic trig. formulas.

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