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secondary 4 | A Maths
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Sonia
Sonia

secondary 4 chevron_right A Maths chevron_right Singapore

Morning!!!! can someone please help me with this qns ? Thx youuuu

Date Posted: 8 months ago
Views: 35

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Bern Ong @ 88Tuition
Bern Ong @ 88tuition's answer
102 answers (A Helpful Person)
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Keep Trying, you can do it;)
Eric Nicholas K
Eric Nicholas K
8 months ago
One correction. Cos theta/2 cannot stay +-. This is because theta/2 is guaranteed to be between 90 and 135 and so its cosine will have a negative value.
Bern Ong @ 88Tuition
Bern Ong @ 88Tuition
8 months ago
Good Catch, Thank you Eric. ;)
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DAI BIN
Dai Bin's answer
78 answers (Tutor Details)
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Eric Nicholas K
Eric Nicholas K's answer
5238 answers (Tutor Details)
Good morning Sonia! I hope you have made good progress in your revision! Here is my variant of the workings.

I used a basic angle’s triangle instead so that I do not have to worry about where to place the negative signs in the triangle. Instead, I place a negative sign afterwards in front of the sine, cosine or tangent based on my knowledge of A-S-T-C.

We use the double angle formula in both cases and we have to determine the direct quadrant in which the new angles lie in.

Let me know if you need more explanation and I will do my best to explain them again.
Sonia
Sonia
8 months ago
Thank you so much Eric! I’ve made some improvements and i’m so happy! i hope i can perform well in my upcoming Os :(