Re: Solve Equation
- To: mathgroup at smc.vnet.net
- Subject: [mg20855] [mg20855] Re: [mg20813] Solve Equation
- From: Andrzej Kozlowski <andrzej at tuins.ac.jp>
- Date: Wed, 17 Nov 1999 03:41:21 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
This is not surprising since: In[1]:= L = 7; b = Pi/3 ; a = Pi/3*5; In[2]:= {L == 5 + 4Cos[a], L == 13 - 12 Cos[b], L == 10 - 3Cos[a + b]} Out[2]= {True, True, False} I get the following answers using NSolve: In[1]:= a /: Cos[a] = (1 - t^2)/(1 + t^2); a /: Sin[a] = (2t)/(1 + t^2); In[2]:= b /: Cos[b] = (1 - s^2)/(1 + s^2); b /: Sin[b] = (2s)/(1 + s^2); In[3]:= {L, Cos[a], Cos[b]} /. NSolve[{L == 5 + 4Cos[a], L == 13 - 12 Cos[b], L == 10 - 6TrigExpand[Cos[a + b]]}, {t, s, L}] Out[3]= {{27.8341 + 0. I, 5.70853, -1.23618}, {27.8341 + 0. I, 5.70853, -1.23618}, {8.94378, 0.985946, 0.338018}, {8.94378, 0.985946, 0.338018}, {5.22209, 0.055523, 0.648159}, {5.22209, 0.055523, 0.648159}} Hence the solutions are L= 8.94378,Cos[a]= 0.985946,Cos[b]= 0.338018, and L= 5.22209,Cos[a]= 0.055523 ,Cos[b]= 0.648159. Solve also gives solutions but they look very complicated. But then parhaps your equations were wrong. Replacing 3 by 6 in the last one gives the answer you wanted: In[4]:= {L, Cos[a], Cos[b]} /. Solve[{L == 5 + 4Cos[a], L == 13 - 12 Cos[b], L == 10 - 3TrigExpand[Cos[a + b]]}, {t, s, L}] Out[4]= 1 1 1 1 1 1 {{7, -, -}, {7, -, -}, {9, 1, -}, {9, 1, -}} 2 2 2 2 3 3 -- > From: "Mecit Yaman" <mecit at iname.com> To: mathgroup at smc.vnet.net > Date: Sun, 14 Nov 1999 18:14:01 -0500 (EST) > To: mathgroup at smc.vnet.net > Subject: [mg20855] [mg20855] [mg20813] Solve Equation > > i am trying to solve 3 equations on 3 variables. Mathematica is complaining > about trigonometric functions, sin and cosine. > > L= 5+4Cos[a] > L=13-12 Cos[b] > L=10 - 6Cos[a+b] > > I tried to change > Cos[a] -> x > Cos[b] -> y > Cos[a+b] - > (x y - Sqrt[1-x x]Sqrt[1- y y]) > > But this time it only gives me a trivial solution.(L=0) > I am trying to get the solution. > > L=7, b=Pi/3 , a= Pi/3*5 > > Good work , everyone. > Mecit > MSc student @ University of Cape Town > > > >