C3 Trigonometry advice Watch

Sir_Malc
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I need some advice with Core 3 trigonometry. I have asked my teacher all these questions but she is new and can't really explain that well.

Since starting core 3 our new teacher has been using the cast diagram for most trig questions. Now, my previous teacher last year taught us core 2 only using rules such as sin^-1(.5)=30 degrees then just plus or subtract 360 degrees to get all the answers in the range specified. Similar methods for cos and tan.

However, we've started doing some questions in core 3 where we have to work out answers in exact surd form and sometimes the edexcel workbook asks you to work out values of sec, cosec and cot without using a calculator and suddenly I'm expected to know how the cast diagrams works with these angles and also how they relate to right angles triangles with SOHCAHTOA.

Worse is my teacher said I'm expected to know sin cos and tan of certain angles like 30, 45 and 60 degrees in surd form already. But I've never had to learn this before. and every question I come across I've been able to type it into the calculator and it gives it in surd form anyway?

I guess my question's are, do I need to learn the cast diagram as it plays a more important role than just finding a value from sin cos tan like in C2?

Do I need to learn these 30, 45 and 60 degree angles so I can 'break down' certain angles later on?
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Mr M
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(Original post by Sir_Malc)
I need some advice with Core 3 trigonometry. I have asked my teacher all these questions but she is new and can't really explain that well.

Since starting core 3 our new teacher has been using the cast diagram for most trig questions. Now, my previous teacher last year taught us core 2 only using rules such as sin^-1(.5)=30 degrees then just plus or subtract 360 degrees to get all the answers in the range specified. Similar methods for cos and tan.

However, we've started doing some questions in core 3 where we have to work out answers in exact surd form and sometimes the edexcel workbook asks you to work out values of sec, cosec and cot without using a calculator and suddenly I'm expected to know how the cast diagrams works with these angles and also how they relate to right angles triangles with SOHCAHTOA.

Worse is my teacher said I'm expected to know sin cos and tan of certain angles like 30, 45 and 60 degrees in surd form already. But I've never had to learn this before. and every question I come across I've been able to type it into the calculator and it gives it in surd form anyway?

I guess my question's are, do I need to learn the cast diagram as it plays a more important role than just finding a value from sin cos tan like in C2?

Do I need to learn these 30, 45 and 60 degree angles so I can 'break down' certain angles later on?
No and no (but recognising certain trig ratios can be useful).
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brianeverit
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(Original post by Sir_Malc)
I need some advice with Core 3 trigonometry. I have asked my teacher all these questions but she is new and can't really explain that well.

Since starting core 3 our new teacher has been using the cast diagram for most trig questions. Now, my previous teacher last year taught us core 2 only using rules such as sin^-1(.5)=30 degrees then just plus or subtract 360 degrees to get all the answers in the range specified. Similar methods for cos and tan.

However, we've started doing some questions in core 3 where we have to work out answers in exact surd form and sometimes the edexcel workbook asks you to work out values of sec, cosec and cot without using a calculator and suddenly I'm expected to know how the cast diagrams works with these angles and also how they relate to right angles triangles with SOHCAHTOA.

Worse is my teacher said I'm expected to know sin cos and tan of certain angles like 30, 45 and 60 degrees in surd form already. But I've never had to learn this before. and every question I come across I've been able to type it into the calculator and it gives it in surd form anyway?

I guess my question's are, do I need to learn the cast diagram as it plays a more important role than just finding a value from sin cos tan like in C2?

Do I need to learn these 30, 45 and 60 degree angles so I can 'break down' certain angles later on?
Maybe not essential but I would certainly recommend it.
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Sir_Malc
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So how come the edexcel C3 workbook has worked examples where they use the CAST diagram to find out if an answer will be positive or negative?

Here is an example: arctan(sqrt/3):

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Isn't it much easier to simply use tan^-1(sqrt/3)?

I feel like they are teaching it this way for a reason but can't figure out why?
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TenOfThem
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(Original post by Sir_Malc)
INow, my previous teacher last year taught us core 2 only using rules such as sin^-1(.5)=30 degrees then just plus or subtract 360 degrees to get all the answers in the range specified. Similar methods for cos and tan.

(Original post by Sir_Malc)

Isn't it much easier to simply use tan^-1(sqrt/3)?

Firstly - there are at least 3 methods commonly used to find the second solution within the first 360 cycle

Secondly - you really should recognise the trig ratios for 30, 45, and 60

Thirdly - if you provisos teacher only taught you the above - they did not teach you very well
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