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# Basic Trigonometry Tweet

Maths and statistics discussion, revision, exam and homework help.

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IMPORTANT: You must wait until midnight (morning exams)/4.30AM (afternoon exams) to discuss Edexcel exams and until 1pm/6pm the following day for STEP and IB exams. Please read before posting, including for rules for practical and oral exams. 28-04-2013
1. Re: Basic Trigonometry
(Original post by raheem94)
See the diagram below:

Use sin in the blue triangle and you are done.

Spoiler:
Show

brilliant! one question and sorry if it is a bit of a stupid one but the line r that you drew from the side AO to the middle you labelled it a right angle, how comes wouldn't the right angle be on the other side ?
Last edited by Roshniroxy; 28-04-2012 at 13:54.
2. Re: Basic Trigonometry
(Original post by Roshniroxy)
brilliant! one question and sorry if it is a bit of a stupid one but the line r that you drew from the side AO to the middle you labelled it a right angle, how comes wouldn't the right angle be on the other side ?
It is a right angled triangle because it is a tangent to the circle.

I don't understand what you mean by 'other side'?
3. Re: Basic Trigonometry
(Original post by raheem94)
It is a right angled triangle because it is a tangent to the circle.

I don't understand what you mean by 'other side'?
Attached Thumbnails

4. Re: Basic Trigonometry
(Original post by Roshniroxy)
No, this angle won't be a right angle.

Remember tangents make an angle of 90degree with the radius of the circle, hence the other angle was a right angle.

So we know one angle is 90 degree and one is 30 degree, so this angle will be 180-(90+30)=180-120=60deg.
5. Re: Basic Trigonometry
(Original post by raheem94)
No, this angle won't be a right angle.

Remember tangents make an angle of 90degree with the radius of the circle, hence the other angle was a right angle.

So we know one angle is 90 degree and one is 30 degree, so this angle will be 180-(90+30)=180-120=60deg.
Thank you for this !