# Math Is Fun Forum

Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫  π  -¹ ² ³ °

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

RauLiTo
Member
From: Bahrain
Registered: 2006-01-11
Posts: 142

### without the calculater

get the value of :
sin 75 + sin 25

ImPo\$\$!BLe = NoTH!nG
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## #2 2007-01-19 19:58:02

RauLiTo
Member
From: Bahrain
Registered: 2006-01-11
Posts: 142

### Re: without the calculater

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 )

ImPo\$\$!BLe = NoTH!nG
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## #3 2007-01-20 00:21:44

RauLiTo
Member
From: Bahrain
Registered: 2006-01-11
Posts: 142

### Re: without the calculater

guys ?!

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

luca-deltodesco
Member
Registered: 2006-05-05
Posts: 1,470

### Re: without the calculater

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

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The End Of All Things To Come.

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

RauLiTo
Member
From: Bahrain
Registered: 2006-01-11
Posts: 142

### Re: without the calculater

oooh thanks alot luca .... anybody else ?

ImPo\$\$!BLe = NoTH!nG
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## #6 2007-01-20 06:53:34

luca-deltodesco
Member
Registered: 2006-05-05
Posts: 1,470

### Re: without the calculater

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

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

RauLiTo
Member
From: Bahrain
Registered: 2006-01-11
Posts: 142

### Re: without the calculater

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

ImPo\$\$!BLe = NoTH!nG
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## #8 2007-01-20 07:53:48

Toast
Real Member
Registered: 2006-10-08
Posts: 1,321

### Re: without the calculater

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.

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

Stanley_Marsh
Member
Registered: 2006-12-13
Posts: 345

### Re: without the calculater

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.

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

RauLiTo
Member
From: Bahrain
Registered: 2006-01-11
Posts: 142

### Re: without the calculater

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

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