Author Topic: maths doubts....  (Read 1347 times)

Offline helllife

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maths doubts....
« on: November 21, 2009, 10:10:31 am »
question is ...
express this in terms of ratios of acute angles
cos(165)

i know this is simple one...but i just didnt understand how to find it...

Offline slvri

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Re: maths doubts....
« Reply #1 on: November 21, 2009, 10:19:42 am »
u know the rule cosx =-cos(180-x)
so cos165=-cos(180-65)=-cos15
i hate A level...........

Offline helllife

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Re: maths doubts....
« Reply #2 on: November 21, 2009, 11:19:39 am »
oh really? is there such a rules like this? can u please give more rule? like about sin?

Offline astarmathsandphysics

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Re: maths doubts....
« Reply #3 on: November 21, 2009, 11:35:55 am »
It is cosx=-cos(180-x)
Sinx=Sin(180-x)

Offline slvri

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Re: maths doubts....
« Reply #4 on: November 21, 2009, 11:38:29 am »
sinx=sin(180-x)
cosx=-cos(180-x)
tanx=-tan(180-x)
sin(90-x)=cosx
cos(90-x)=sinx
tan(90-x)=1/tanx
sin(-x)=-sinx
cos(-x)=cosx
tan(-x)=-tanx
i hate A level...........

Offline helllife

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Re: maths doubts....
« Reply #5 on: November 21, 2009, 12:45:08 pm »
thank you very much!!!  :)

Offline slvri

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Re: maths doubts....
« Reply #6 on: November 21, 2009, 01:15:05 pm »
and also
sin(x+360)=sinx
cos(x+360)=cosx
tan(x+180)=tanx
there are many more but ive forgotten them
and ur welcome ;)
« Last Edit: November 21, 2009, 04:37:56 pm by slvri »
i hate A level...........

Offline helllife

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Re: maths doubts....
« Reply #7 on: November 21, 2009, 04:05:27 pm »
hey what about
sin(180+x), cos(180+x), tan(180+x)??

Offline astarmathsandphysics

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Re: maths doubts....
« Reply #8 on: November 21, 2009, 04:37:49 pm »
Will post when i get home. There are some useful formulae.

Offline slvri

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Re: maths doubts....
« Reply #9 on: November 21, 2009, 04:42:52 pm »
hey what about
sin(180+x), cos(180+x), tan(180+x)??
oh sory..........tan(180+x)=tanx
and sin(180+x)=-sinx
and cos(180+x)=-cosx
i hate A level...........

Offline astarmathsandphysics

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Re: maths doubts....
« Reply #10 on: November 21, 2009, 05:24:19 pm »
Ok but Sin(180+x)=-Sinx

Offline helllife

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Re: maths doubts....
« Reply #11 on: November 21, 2009, 09:09:26 pm »
thank u very much!! i really appreciated it! :)