| codeshepherd | kmh: Is it not more problem specific ? or some kind of convention.. which we really need not bother.. |
| kmh | TRWBW : i'm not saying it is the only true one, i'm saying in R there is a common convention, for C there is not |
| TRWBW | kmh: yes, and if you asked different people whether there was a common convention or not, some would say yes, some no, some of those who said yes would say different things about what the convention was |
| kmh | codeshepherd : well yes if the nature of your problem indicates a default branch/restriction TRWBW : thatmeans there is none TRWBW : however you will have difficulties to find any standard math book that defines sqrt differently in R |
| TRWBW | kmh: i'm not gonna argue against your opinion, especially if your opinion is that your opinion isn't an opinion but somehow objective truth |
| kmh | TRWBW : it hasn't much to do with that TRWBW : if you don't believe pick up math books and check for yourself how the sqrt is defined for the reals |
| happytron | brick_: did you ever get that shape visualized? |
| brick_ | Okay, so for the 3-variable function f(x,y,z)=z*ln(x*y), x*y must be > 0 and so x and y either both must be negative or both must be positive. Then the domain of this function would be all points that are in both the quadrant I and quadrant III on the x-y plane. (no complex #s) |
| TRWBW | brick_: yup |
| kmh | brick_ : and since that can be z can be anything, you can also give the octants(?) in a 3d coordinate system |
| brick_ | Now when I come to finding the domain of f(x,y,z)=Sqrt[x^2+y^2-z^2-9] i'm stumped. I understand x^2+y^2-z^2-9 must be >0 but what does this mean "geometrically" as per the last problem? |
| happytron | brick_: i would let r^2 = x^2 + y^2, and consider the locus of points satisfying r^2 - z^2 - 9 >= 0 brick_: the problem is radially symmetric about the z-axis |
| kmh | brick_ : do you have a function plotter ? |
| TRWBW | brick_: you could also view that as x^2+y^2-[z^2+9] >=0 <=> x^2+y^2>=z^2+9 |
| kmh | brick_ : it helps you visualize if you just plot the "border", i.e. x^2+y^2-z^2-9=0 |
| happytron | can the mathbot be made to generate plots? |
| dn4 | how would I do sin(1)cos(-1)?? is sin(1) = pi/2 ? |
| brick_ | ok, I think i've got it. thanks all |
| dn4 | same here :D |
| kmh | hehe |
| dn4 | a=0=1-1=(pi/2)-(pi/2) |
| TRWBW | dn4: sin(1)*cos(-1)=(1/2)*sin(2) |
| kmh | dn4 : sin(1) != pi/2 arcsin(1)=Pi/2 |
| dn4 | TRWBW no clue how you got that |
| codeshepherd | errr.. what is the number with no meaning .. err the one that comes in a science fiction.. where a high performance computer will calculate !! I neither read the novel.. and i don't know the story |
| kmh | dn4 : he used the addition theorem |
| TRWBW | codeshepherd: 42, always, 42 codeshepherd: the only number in science fiction stories is 42 |
| kmh | dn4 : a useful site for you : http://en.wikipedia.org/wiki/Trigonometric_identities |
| codeshepherd | ya.. answer to life 42 :) |
| Syzygy- | While your at it, calculate 42!! :P |
| dn4 | *sigh* and to think I passed trig in college |
| kmh | codeshepherd : and it took deep thought 7 million years or so:) |