Question about Solve

08252015, 07:16 AM
(This post was last modified: 08252015 07:22 AM by salvomic.)
Post: #1




Question about Solve
hi,
an Italian student asked to me what's the best way to solve these equations in Solve: E1: A*(2*π*10)*COS(P)+11*A*SIN(P) = 0 E2: 11*A*COS(P)A*(2*π*10)*SIN(P) = 23 where A is amplitude, P phase, the rest 2*PI*frequency (here 10 Hz) I suggest only to set the Prime in DEG mode (he is to get something like 0.36 and 80°, he said). I get different values with different invite suggestion for A and P (but they are values MOD 360, I think), however also about 0 and about 99.93 (giving A=0.001); giving for A 2 and for P 0 I get about 0 and about 80 also... For examples the student got 20350160.0698 whit his tries: 20350160.0698 MOD 360 is about 280 (about 279.93), that's 36080... Whit my values (about 0.36 and 99.93) the equations are consistent but a negative amplitude hasn't a physic sense. But the guy is searching a general good solution if he doesn't know what invite values to give... Suggestions? Salvo ∫aL√0mic (IT9CLU) :: HP Prime 50g 41CX 71b 42s 39s 35s 12C 15C  DM42, DM41X  WP34s Prime Soft. Lib 

08252015, 10:27 AM
Post: #2




RE: Question about Solve
when i remember correct, Setting the angular mode to deg isn't a good aproach. This should be best in radians.
regards Wolfgang 

08252015, 10:29 AM
Post: #3




RE: Question about Solve
(08252015 10:27 AM)ww63 Wrote: when i remember correct, Setting the angular mode to deg isn't a good aproach. This should be best in radians. hi Wolfgang, you're right, but in this problem he must calculate phase in DEG (sin, cos), as usually speaking about electricity... Salvo ∫aL√0mic (IT9CLU) :: HP Prime 50g 41CX 71b 42s 39s 35s 12C 15C  DM42, DM41X  WP34s Prime Soft. Lib 

08252015, 12:44 PM
Post: #4




RE: Question about Solve  
08252015, 12:47 PM
Post: #5




RE: Question about Solve
(08252015 12:44 PM)roadrunner Wrote: Hi Salvo, in fact, Road! this is the actual solution: an infinite number of solutions. Thank you, I'll say about this to the student. Salvo ∫aL√0mic (IT9CLU) :: HP Prime 50g 41CX 71b 42s 39s 35s 12C 15C  DM42, DM41X  WP34s Prime Soft. Lib 

08252015, 02:00 PM
(This post was last modified: 08252015 02:03 PM by DrD.)
Post: #6




RE: Question about Solve
(08252015 07:16 AM)salvomic Wrote: hi, Here is the solution he was seeking (Advanced Graphing App with X=P, Y=A): 

08252015, 03:43 PM
Post: #7




RE: Question about Solve
(08252015 02:00 PM)DrD Wrote: Here is the solution he was seeking (Advanced Graphing App with X=P, Y=A): thank you Dale, this is the solution he was seeking, however, as Road wrote, it shouldn't be unique... Salvo ∫aL√0mic (IT9CLU) :: HP Prime 50g 41CX 71b 42s 39s 35s 12C 15C  DM42, DM41X  WP34s Prime Soft. Lib 

08252015, 07:50 PM
Post: #8




RE: Question about Solve
There was no mention of boundary conditions in the problem, but you did mention an electrical context. The important solution he was after occurs in the first 90°, and is periodic forevermore. Since the phase is constant, after the first cycle there wouldn't be much point in reporting periodic values for subsequent cycles. For this problem, perhaps that's why he was seeking that particular result(?)


08252015, 07:52 PM
Post: #9




RE: Question about Solve
(08252015 07:50 PM)DrD Wrote: There was no mention of boundary conditions in the problem, but you did mention an electrical context. The important solution he was after occurs in the first 90°, and is periodic forevermore. Since the phase is constant, after the first cycle there wouldn't be much point in reporting periodic values for subsequent cycles. For this problem, perhaps that's why he was seeking that particular result(?) yes, you're right. So, 80° is the right solution, I think he would to find only this one. Salvo ∫aL√0mic (IT9CLU) :: HP Prime 50g 41CX 71b 42s 39s 35s 12C 15C  DM42, DM41X  WP34s Prime Soft. Lib 

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