noz92 Posted October 13, 2004 Share Posted October 13, 2004 After studying the functions on my scientific calculator, I came across sin and cos. I've heard people talking about them on NASA TV, but never learned what it was. Could somebody explain them to me? Link to comment Share on other sites More sharing options...

Cap'n Refsmmat Posted October 13, 2004 Share Posted October 13, 2004 Sine and Cosine are trigonometry (trigonomitrical?) functions. sorry, having trouble making the definitions and latex, so try Wikipedia: http://en.wikipedia.org/wiki/Sine Link to comment Share on other sites More sharing options...

ydoaPs Posted October 13, 2004 Share Posted October 13, 2004 they are ratios of the sides of a right triangle. like the sine of 60degrees is 1/2. sine(sin) is opposite side over hypotenuse cosecant(csc) is the inverse of sin. it is hypotenuse over opposite side cosine(cos) is the cofunction of sine. it is adjacent side over hypotenuse secant(sec) is the inverse of cosine. it is hypotenuse over adjacent side tangent(tan) is opposite side over adjacent side. cotangent(cot) is both the inverse and cofunction of tangent. it is adjacent side over opposite side in the first quadrant, all six trig functions are positive in the second quadrant, sine and cosecant are positive while the rest are negative in the third quadrant, tangent and cotangent are positive while the rest are negative in the forth quadrant, cosine and secant are positive while the rest are negative Link to comment Share on other sites More sharing options...

Dave Posted October 13, 2004 Share Posted October 13, 2004 Erm, I think you'll find that csc, sec and cot are not the inverses of their associated functions. Rather, [math]\csc(x) = \frac{1}{\sin(x)}[/math], [math]\sec(x) = \frac{1}{\cos(x)}[/math], and [math]\cot(x) = \frac{1}{\tan(x)}[/math] Inverse functions are arcsin, arccos and arctan respectively. Totally different things. Link to comment Share on other sites More sharing options...

ydoaPs Posted October 14, 2004 Share Posted October 14, 2004 sorry, wrong word. what are they then? if i hit sin then the inverse button on my calc, i get the csc of what i put in for sin. what was the word for them then? reciprocal functions? Link to comment Share on other sites More sharing options...

AL Posted October 14, 2004 Share Posted October 14, 2004 if i hit sin then the inverse button on my calc, i get the csc of what i put in for sin. what was the word for them then? reciprocal functions? The inverse you are thinking of is the "multiplicative inverse," which is the same thing as reciprocal. For a nonzero number x, its multiplicative inverse is 1/x. This is different from an inverse function. For a function f(x), its inverse is a function g(x) such that f(g(x)) = 1 for all x. Link to comment Share on other sites More sharing options...

pulkit Posted October 14, 2004 Share Posted October 14, 2004 How is calculation of sine and cosine hardwired ? Do you go about exploiting series expansion or do you use a definate integral ? Link to comment Share on other sites More sharing options...

Woxor Posted October 14, 2004 Share Posted October 14, 2004 How is calculation of sine and cosine hardwired ? Do you go about exploiting series expansion or do you use a definate integral ?I think they use taylor series and such, but I'm not that sure. I don't think that strictly numerical methods would work in general since most of them require the calculation of the function value or its derivative (which defeats the point in this case). Link to comment Share on other sites More sharing options...

Dave Posted October 14, 2004 Share Posted October 14, 2004 I've heard that they will generally use some form of Taylor expansion to give the desired degree of accuracy. Link to comment Share on other sites More sharing options...

pulkit Posted October 15, 2004 Share Posted October 15, 2004 So is calculation of sin and cos hardwired or is it computed using simpler operations ? Link to comment Share on other sites More sharing options...

Woxor Posted October 15, 2004 Share Posted October 15, 2004 So is calculation of sin and cos hardwired or is it computed using simpler operations ?Even though I obviously don't know enough about this to justify trying to answer twice, here goes: if by "hardwired" you mean that the calculator simply stores a huge array of ordered pairs corresponding to a sine or cosine function so that the input number is matched with the appropriate output number (rather than it being calculated by the computer upon execution), no, I'm almost positive that it's not done that way. In fact, I believe that sin and cos functions in one of the C math libraries can take a long time to compute (compared to the basic +, -, *, / operators), which would indicate that a calculation (such as a taylor series) is being performed. But when you look at the functions, there's a shockingly small range of values that need be calculated -- all you really need is one quarter of a period (e.g. the part from sin(0) to sin(pi/2)), since the rest of the function, or both, actually, is/are composed of identical curves that have been flipped around. So they may only need a few terms of the Taylor series to get decent accuracy. So yeah, I'd say it's a bunch of simple polynomial operations, like ".4-.4*.4*.4/6+.4*.4*.4*.4*.4/120" or something. Link to comment Share on other sites More sharing options...

NSX Posted October 16, 2004 Share Posted October 16, 2004 heh I'm pretty sure they use the Taylor expansion. It's actually quite funny when I input a large sum of sines & cosines into my scientific calculator, and it returns an "Error 3" Link to comment Share on other sites More sharing options...

pulkit Posted October 17, 2004 Share Posted October 17, 2004 Even though I obviously don't know enough about this to justify trying to answer twice' date=' here goes: if by "hardwired" you mean that the calculator simply stores a huge array of ordered pairs corresponding to a sine or cosine function so that the input number is matched with the appropriate output number (rather than it being calculated by the computer upon execution), no, I'm almost positive that it's not done that way. In fact, I believe that sin and cos functions in one of the C math libraries can take a long time to compute (compared to the basic +, -, *, / operators), which would indicate that a calculation (such as a taylor series) is being performed. But when you look at the functions, there's a shockingly small range of values that need be calculated -- all you really need is one quarter of a period (e.g. the part from sin(0) to sin(pi/2)), since the rest of the function, or both, actually, is/are composed of identical curves that have been flipped around. So they may only need a few terms of the Taylor series to get decent accuracy. So yeah, I'd say it's a bunch of simple polynomial operations, like ".4-.4*.4*.4/6+.4*.4*.4*.4*.4/120" or something.[/quote'] I did not mean a ROM when I said hardwired. I meant more of an electronic circuit that does sin/cos calculation. ( Think of adders, dividers, sqare root calculators etc. ) Link to comment Share on other sites More sharing options...

Dave Posted October 18, 2004 Share Posted October 18, 2004 I don't think so. You can derive sin/cos quite accurately and quickly without having dedicated circuits. As far as I'm aware, basic calculators usually have only the most basic of operations, namely addition and multiplication and from those you can derive every other function on the calculator. Link to comment Share on other sites More sharing options...

WaR Posted October 18, 2004 Share Posted October 18, 2004 Actually, I recently had a discussion with a graduate student and he was telling me that we calculate sines and cosines with Taylor series, but the calculator does not use this. Calculators use a variable storing system and a program called CORDIC. The explanation he gave was kind of abstract, but at least now I'm sure the calculator does not use approximations or Taylor. Link to comment Share on other sites More sharing options...

fuhrerkeebs Posted October 18, 2004 Share Posted October 18, 2004 Yes, Taylor series is slow and has a limited range. It's much more common to use an iterative algorithm that locates the position of a point x degress from the axis on a circle, and derives the sin and cosine from that, or, as has been mentioned above, the CORDIC algorithm. To generalize, CORDIC is an iterative process that usually uses a tangent table, but can also be done with smaller and smaller vector rotations. You can read about it here: http://www.worldserver.com/turk/computergraphics/FixedPointTrigonometry.pdf Link to comment Share on other sites More sharing options...

fuhrerkeebs Posted October 18, 2004 Share Posted October 18, 2004 As a side note, CORDIC can also be used to calculate functions other that sine and cosine, such as logarithms and square roots. Link to comment Share on other sites More sharing options...

Dave Posted October 18, 2004 Share Posted October 18, 2004 Looks like I was wrong then Link to comment Share on other sites More sharing options...

fuhrerkeebs Posted October 18, 2004 Share Posted October 18, 2004 Hahaha only partially--alot of free mathematica-like programs use Taylor series still, such as Maxima Link to comment Share on other sites More sharing options...

pulkit Posted October 19, 2004 Share Posted October 19, 2004 How hard is it to make a dedicated square root or sin/cos circuit ? I intend to make a digital electronics project by the end of the week, I was thinking of building one of the above. Link to comment Share on other sites More sharing options...

noz92 Posted January 5, 2005 Author Share Posted January 5, 2005 I understand that [math]\sin = \frac{opposite}{hypotonuse}[/math], and the other ones, but what do we use to find the leanths of opposite and hypotonuse. [math]\sin 76 \thickaprox 0.929776485[/math], and [math]\cos 76 \thickaprox 0.368124552[/math], I understand that and all the others, but what unit of mesurement do we use to find the leanths of the opposite, hypotonuse, and adjecent sides? Link to comment Share on other sites More sharing options...

ydoaPs Posted January 5, 2005 Share Posted January 5, 2005 I understand that and all the others, but what unit of mesurement do we use to find the leanths of the opposite, hypotonuse, and adjecent sides? whatever you want. m, cm, in., ft, mi, km, ... you don't have enough info with just an angle and it's sine/cosine to find solve the triangle. Link to comment Share on other sites More sharing options...

noz92 Posted January 5, 2005 Author Share Posted January 5, 2005 What more information do I need? Link to comment Share on other sites More sharing options...

ydoaPs Posted January 5, 2005 Share Posted January 5, 2005 at least another side. law of sines [math]\frac{a}{sin\alpha}=\frac{b}{sin\beta}=\frac{c}{sin\gamma}[/math] law of cosines [math]c_^2=a^2+b^2-2ab(cos\gamma)[/math] a thing i like about the law of cosines is that if you put a right angle in for [math]\gamma[/math], you get the pythagorean theorem. Link to comment Share on other sites More sharing options...

noz92 Posted January 7, 2005 Author Share Posted January 7, 2005 What are all of the greek letters representing? And what's wrong with the LaTeX? Link to comment Share on other sites More sharing options...

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