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# C1/C2 Trig Question HELP! watch

1. Given that angle A is reflex and cosA = root13 / 7
(a) find the exact value of sinA
(b) find the exact value of tanA

I generally understand the question but I need someone to explain the angles and signs to me. If angle A is in quadrant 3 then shouldn't cosA= - root13/7?
2. (Original post by Anon736)
Given that angle A is reflex and cosA = root13 / 7
(a) find the exact value of sinA
(b) find the exact value of tanA

I generally understand the question but I need someone to explain the angles and signs to me. If angle A is in quadrant 3 then shouldn't cosA= - root13/7?
It'll be in the 4th quadrant surely?
3. (Original post by Anon736)
Given that angle A is reflex and cosA = root13 / 7
(a) find the exact value of sinA
(b) find the exact value of tanA

I generally understand the question but I need someone to explain the angles and signs to me. If angle A is in quadrant 3 then shouldn't cosA= - root13/7?
Reflex angles are greater than 180 degrees, but are also less than 360 degrees so A could be in the fourth quadrant, making it positive.
4. (Original post by NiamhM1801)
It'll be in the 4th quadrant surely?
Well actually thats a good question because a reflex is greater than 180 so I actually don't know if its quadrant 3 or 4.
5. (Original post by Anon736)
Given that angle A is reflex and cosA = root13 / 7
(a) find the exact value of sinA
(b) find the exact value of tanA

I generally understand the question but I need someone to explain the angles and signs to me. If angle A is in quadrant 3 then shouldn't cosA= - root13/7?
Reflex angle covers both 3rd and 4th quadrant since refle angle is angle bigger than π. So this tells you that in fact angle A is in fact in the 4th quadrant. So sinA will be negative and so will tanA - just sketch the graphs and you will see this.
6. (Original post by h3rmit)
Reflex angles are greater than 180 degrees, but are also less than 360 degrees so A could be in the fourth quadrant, making it positive.
For a question like this how do you know which one to use?
7. (Original post by Anon736)
For a question like this how do you know which one to use?
cosA is positive, therefore it has to be in the 4th. Remember the diagram
8. (Original post by B_9710)
Reflex angle covers both 3rd and 4th quadrant since refle angle is angle bigger than π. So this tells you that in fact angle A is in fact in the 4th quadrant. So sinA will be negative and so will tanA - just sketch the graphs and you will see this.
But why can it not be in the 3rd quadrant?
9. (Original post by NiamhM1801)
cosA is positive, therefore it has to be in the 4th. Remember the diagram
ahhhhhhh

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