Eric Nicholas K's answer to Vignesh anand's Secondary 3 A Maths Singapore question.
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Interestingly I did not obtain 90 at all this time.
Date Posted:
3 years ago
Thanks Mr Eric. I will send my working. Let me know where I am wrong. I send my working as a question (photo)
A and B are acute angles such that cos ( A-B) =4/5 and SinASinB =1/5.
Mr Eric, pls explain why the condition that A and B are acute angles has to be specified in the question?
Mr Eric, pls explain why the condition that A and B are acute angles has to be specified in the question?
Now, it could well be the case where A is, for example, a third quadrant angle of 200 and B is a second quadrant angle of 163, so that the angle difference is 37 (and cos 37 is roughly 4/5).
Supposing this is the case, then sin A would be negative while sin B would be positive. Their product is negative in this instance, unlike the given 1/5.
This is why the question must state that both A and B are acute, to avoid such ambiguities.
Supposing this is the case, then sin A would be negative while sin B would be positive. Their product is negative in this instance, unlike the given 1/5.
This is why the question must state that both A and B are acute, to avoid such ambiguities.
Oh ok
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