without the calculater

RauLiTo · 2007-01-19 19:19:55

get the value of :
sin 75 + sin 25

RauLiTo · 2007-01-19 19:58:02

i got sin 75 but the problem with sin 25

sin 75 = sin ( 45 + 30 ) = sin 45 cos 30 + cos 45 sin 30 = ( √ 3 + 1 ) / ( 2 √ 2 )

RauLiTo · 2007-01-20 00:21:44

guys ?!

luca-deltodesco · 2007-01-20 05:26:31

i tried but i cant think of anyway of getting sin 25

RauLiTo · 2007-01-20 06:52:58

oooh thanks alot luca .... anybody else ?

luca-deltodesco · 2007-01-20 06:53:34

lol i was about to answer for sin 75, but just after i posted it, you had posted yours, so i just deleted it

RauLiTo · 2007-01-20 07:21:59

heheheh ooh
we want the sin 25 now or maybe there is a different way

Toast · 2007-01-20 07:53:48

I wikipedia-ed exact trigonometric constants and it said:

Wikipedia wrote:

All values of sine, cosine, and tangent of angles with 3° increments are derivable using identities: Half-angle, Double-angle, Addition/subtraction and values for 0°, 30°, 36° and 45°. Note that 1° = π/180 radians.

As 25 degrees is not divisible by 3, I would presume that there is no exact value for it. Although I must say, I'm not an expert in this area.

Stanley_Marsh · 2007-01-20 10:58:30

25x3=75
Sin3a= 3sina - 4(sina^3) after simplification(don't know if I am correct) , then just solve the equation.but how to solve it? lol.

RauLiTo · 2007-01-20 23:12:32

thats the question
i know the rule for
sin / cos 3 θ but i dont know how to use it !

Math Is Fun Forum

#1 2007-01-19 19:19:55

without the calculater

#2 2007-01-19 19:58:02

Re: without the calculater

#3 2007-01-20 00:21:44

Re: without the calculater

#4 2007-01-20 05:26:31

Re: without the calculater

#5 2007-01-20 06:52:58

Re: without the calculater

#6 2007-01-20 06:53:34

Re: without the calculater

#7 2007-01-20 07:21:59

Re: without the calculater

#8 2007-01-20 07:53:48

Re: without the calculater

#9 2007-01-20 10:58:30

Re: without the calculater

#10 2007-01-20 23:12:32

Re: without the calculater

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