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Need to solve this

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Abdullah Azzam
Abdullah Azzam on 1 Jun 2019
Closed: MATLAB Answer Bot on 20 Aug 2021
Hi guys I need away to solve these 3 equations and get the value of a b and c
a+b = 204
a+b*exp(-105*c) = 192.6
a+b*exp(-180*c) = 177.6
I have tried to use vpasolve but it gives wrong answer. What other way to use?

Answers (2)

Stephan
Stephan on 1 Jun 2019
I assume you want real Solutions. Then try:
syms a b c
assume ([a b c], 'real')
eq = [a+b == 204;...
a+b*exp(-105*c) == 192.6;...
a+b*exp(-180*c) == 177.6];
[a, b, c] = vpasolve(eq,[a b c])
Best regards
Stephan
  2 Comments
Abdullah Azzam
Abdullah Azzam on 1 Jun 2019
It gives wrong output it just make a=204 and b=0 and solve for c but when you substitute the result back in ghe equations you can varify they are wrong answers
Walter Roberson
Walter Roberson on 12 Jul 2019
vpasolve() works to finite precision according to the digits() setting, and the calculations are suffering from massive loss of precision.
You can give a search range:
[A,B,C] = vpasolve(eq,[a b c],[200 230;-50 -1/2;-5 5])

Alex Sha
Alex Sha on 12 Jul 2019
Hi, How about the results belows:
a: 214.703486863113
b: -10.7034868631133
c: -0.00690634104047918

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