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Radians and Trigonometry. (1 Viewer)

studentcheese

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Find the value of:

cos(2pi/5)cos(3pi/5) - sin(pi/10)sin(9pi/10) - 2sin(3pi/5)cos(pi/10) :angry:

THANK YOU :uhhuh:
 

Trebla

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Find the value of:

cos(2pi/5)cos(3pi/5) - sin(pi/10)sin(9pi/10) - 2sin(3pi/5)cos(pi/10) :angry:

THANK YOU :uhhuh:




Alternatively, the quickest method is just to actually plug it in your calculator LOL!
 

tommykins

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stupid maple didn't recognise my command :mad:
 

Aquawhite

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I have a question for this. In an exam would it suffice just to put the question into the calculator, rather than go through all the writing (it seems a little too much for maybe a question in the HSC exam max 3 marks).

I saw one like this in the 2004 paper. It was only out of 2 so just the calculator would be fine?
 

Iruka

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Considering that the trig identites that Trebla used aren't even in the 2 unit syllabus, I think using the calculator would be just fine.
 

LordPc

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I have a question for this. In an exam would it suffice just to put the question into the calculator, rather than go through all the writing (it seems a little too much for maybe a question in the HSC exam max 3 marks).

I saw one like this in the 2004 paper. It was only out of 2 so just the calculator would be fine?
I'm assuming that this particular problem is from question 1 (possibly question 2) of the hsc paper? there is usually a question very early on that is complex and is simply there to test that you do know how to use a calculator. the question by OP involved a lot of bracket work, one mistake and you get the wrong answer.

so yea, plugging it into the calc would be fine and indeed what would be expected from this question

if however the question used the word show instead of find, ie

Show the value of:

cos(2pi/5)cos(3pi/5) - sin(pi/10)sin(9pi/10) - 2sin(3pi/5)cos(pi/10) = -2


then trebla's answer is what you would need to provide (but im thinking that would be a 3u/4u type question so not to worry ;))

but find usually means they just want a number or quick answer
 

the-derivative

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Considering that the trig identites that Trebla used aren't even in the 2 unit syllabus, I think using the calculator would be just fine.
Yeah I agree that calculator should be fine.
However, what do you mean the formulas aren't in the 2U syllabus.

All he used was the unit circle/properties of trigonometric ratios.
If you have Fitzpatrick 2U - it's on page 164. They call it 'Symmetry Properties of Trigonometric Ratios'.
 

Iruka

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Yeah I agree that calculator should be fine.
However, what do you mean the formulas aren't in the 2U syllabus.

All he used was the unit circle/properties of trigonometric ratios.
If you have Fitzpatrick 2U - it's on page 164. They call it 'Symmetry Properties of Trigonometric Ratios'.

Sorry, I thought that there was the products to sums or sums to products formula in there somewhere (probably cause that's the way that I solved it). Products to sums/sums to products certainly isn't in the 2u syllabus.

BTW, fitzpatrick was originally written for some Victorian course about 30 years ago, so I wouldn't take it as gospel truth concerning what is/isn't in the syllabus.
 

the-derivative

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Sorry, I thought that there was the products to sums or sums to products formula in there somewhere (probably cause that's the way that I solved it). Products to sums/sums to products certainly isn't in the 2u syllabus.

BTW, fitzpatrick was originally written for some Victorian course about 30 years ago, so I wouldn't take it as gospel truth concerning what is/isn't in the syllabus.
I don't.
Besides I do 4U anyway, so I don't really need to differentiate between what is on what syllabus.
 

Aquawhite

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Thanks. I will have to brush up on all the terms: e.g. Show, Evaluate, Find etc. :D Will save me unecessary working out...
 

studentcheese

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Considering that the trig identites that Trebla used aren't even in the 2 unit syllabus, I think using the calculator would be just fine.
oops. My bad. the question is from the 3unit syllabus. I tend to place 2U and 3U stuff together.
 

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