Author Topic: maths doubts.... (Read 1365 times)

helllife · « **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...

slvri · « **Reply #1 on:** November 21, 2009, 10:19:42 am »

u know the rule cosx =-cos(180-x)
so cos165=-cos(180-65)=-cos15

helllife · « **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?

astarmathsandphysics · « **Reply #3 on:** November 21, 2009, 11:35:55 am »

It is cosx=-cos(180-x)
Sinx=Sin(180-x)

slvri · « **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

helllife · « **Reply #5 on:** November 21, 2009, 12:45:08 pm »

thank you very much!!!

slvri · « **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

helllife · « **Reply #7 on:** November 21, 2009, 04:05:27 pm »

hey what about
sin(180+x), cos(180+x), tan(180+x)??

astarmathsandphysics · « **Reply #8 on:** November 21, 2009, 04:37:49 pm »

Will post when i get home. There are some useful formulae.

slvri · « **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

astarmathsandphysics · « **Reply #10 on:** November 21, 2009, 05:24:19 pm »

Ok but Sin(180+x)=-Sinx

helllife · « **Reply #11 on:** November 21, 2009, 09:09:26 pm »

thank u very much!! i really appreciated it!

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