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# January 2012 C3 Trigonometry Q8 HELP NEEDED! Watch

1. Hey, I have been going through past papers and answering all questions on certain topics as a part of my C3/C4 revision. However, I am on my last Trigonometry question (yay!) but I can't seem to do part 8(c)

the question paper is on this link:
http://www.examsolutions.net/a-level...y/paper.php#Q5

I got 8(a) correct and also part (b). However, I can only get one of the solutions on part (c) [the solution I have is 5pi/12]. I am unsure how they arrived at the second sollution [11pi/12] and I am unsure how they arrived at the formula 2pi-feta=feta+pi/6

Any help would be appreciated; thank you!!!
2. (Original post by jessica_anne_clu)
Hey, I have been going through past papers and answering all questions on certain topics as a part of my C3/C4 revision. However, I am on my last Trigonometry question (yay!) but I can't seem to do part 8(c)

the question paper is on this link:
http://www.examsolutions.net/a-level...y/paper.php#Q5

I got 8(a) correct and also part (b). However, I can only get one of the solutions on part (c) [the solution I have is 5pi/12]. I am unsure how they arrived at the second sollution [11pi/12] and I am unsure how they arrived at the formula 2pi-feta=feta+pi/6

Any help would be appreciated; thank you!!!
In part (b) you found an expression for

In part(c), if you divide both sides of the equation by then the LHS is the expression you worked with in part (b).

This means that you now need to solve the equation:

One solution to this is obviously going to be when

which you can rearrange and solve, and check that the value for theta is in the required range.

However, remember that tan is periodic and when you solve tan A = tan B there will be other solutions - you should have covered this as part of your bookwork. All you have to do is check which solutions are going to give you angles in the correct range

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