What's wrong with my solution to this trigo question?

Mikethm SG

Hope either wee_ws or eagle or some kind soul can help me with the above question's solution. I took it from a 2008 prelim paper which took it from a 80s GCE O AM exams.

I just can't agree with the given solution (in box) and I explained my rationale below it.

My solution is the opposite of the answer sheet's.

As I doubt the setter can set a question and give the wrong answer, therefore my answer must be wrong. But I can't figure out why...

So I would appreciate if anyone can point out the flaw in my solution. Thanks.

Lee012lee SG

Hi Mikethm,

The answer sheet's answer is wrong.

Your answer is correct.

The TYS's answer for this question which is June 1995 GCE "O" level Paper 2 Q5(b) question is the same as your answer.

There is a similar question in Pan Pacific Additional Mathematics Textbook Page 300 Question 20(c). The answer is also the same as your answer.

Mikethm SG

Guess I have to assume the answer sheet had a typo.

Thanks.