suppose i have a function sin(sin x)
sin x will give values [-1,1] ...
so now, should i take these values in degree or radian to find sin(sin x) ?

2. The standard "geometric" definition for:

$\sin:\mathbb{R}\to [-1,1],\quad x\to \sin x$

$\cos: \mathbb{R}\to [-1,1],\quad x\to \cos x$

is when $x$ is "measured" in radians. So we have good properties, for example:

(i) $(\sin)'=\cos$

(ii) $\sin x=x-x^3/3!+x^5/5!-\ldots\quad (\forall x\in \mathbb{R})$

etc.

3. I believe you want radians.

4. The only time you should use degrees is when the problem specifically gives angles in degrees. For problems in which sine (or cosine) is used just as a function always use radians.

(There are a number of ways to define sine and cosine that do not involve angles at all. So strictly speaking the argument is not in "radians" or "degrees". However, to be able to identify those functions with the sine and cosine functions we learned in trigonometry, we use radians.)

5. Originally Posted by HallsofIvy
The only time you should use degrees is when the problem specifically gives angles in degrees. For problems in which sine (or cosine) is used just as a function always use radians.

(There are a number of ways to define sine and cosine that do not involve angles at all. So strictly speaking the argument is not in "radians" or "degrees". However, to be able to identify those functions with the sine and cosine functions we learned in trigonometry, we use radians.)
Actually My question is that the output of sine and cosine functions is in degrees or radians

6. Originally Posted by cupid
Actually My question is that the output of sine and cosine functions is in degrees or radians
For every $x\in\mathbb{R}$ it is the case that $\sin(x)\in\mathbb{R}$ and $\cos(x)\in\mathbb{R}$.

7. Originally Posted by Plato
For every $x\in\mathbb{R}$ it is the case that $\sin(x)\in\mathbb{R}$ and $\cos(x)\in\mathbb{R}$.
Isn't it more like ...

$sinx \in [-1,1]$ ???

8. Originally Posted by cupid
Isn't it more like ... $sinx \in [-1,1]$ ???
But $[-1,1]\subset\mathbb{R}$.

The point being that both the sine and cosine functions map real numbers to real numbers.

9. but my question is that ... for example i have a question ... sin (sin x)

i need to calculate the value of this function at $x = \frac{\pi}{2}$

as $sin\frac{\pi}{2} = 1$
now i need to calculate sin(1)

so should i find value of sin(1 radian) or sin(1 degree) ???

10. Originally Posted by cupid
but my question is that ... for example i have a question ... sin (sin x)
i need to calculate the value of this function at $x = \frac{\pi}{2}$
as $sin\frac{\pi}{2} = 1$ now i need to calculate sin(1)
so should i find value of sin(1 radian) or sin(1 degree) ???
I do not know what a degree is.
I know what real numbers are.
1 is a real number.
Thus it is $\sin\left(\sin\left(\frac{\pi}{2}\right)\right)=\s in(1)\approx 0.841$.

11. Originally Posted by Plato
I do not know what a degree is.
I know what real numbers are.
1 is a real number.
Thus it is $\sin\left(\sin\left(\frac{\pi}{2}\right)\right)=\s in(1)\approx 0.841$.
that is for 1 radian ... for 1 degree its like 0.0014 something

12. The point that I think you are missing is that Radians are a pure number! They are defined as the arc length of a circle divided by the radius of the same circle so strictly speaking the "units" (length) reduce out leaving a Real number.

Radian - Wikipedia, the free encyclopedia

13. Yes, that was what I was trying to say to begin with!

"Strictly speaking the argument is not in "radians" or "degrees". However, to be able to identify those functions with the sine and cosine functions we learned in trigonometry, we use radians."