Need help solving two unknown variable equations

2018 8 21
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更新时间：2018 8 22
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Hi, I'm new in matlab. I would like to ask your help how I can solve the unknown variables 'a' and 'b' from the below equations in matlab.
.
I tried using the below method
. .
syms a b
eqn_1 = 20*log((1 + ((20/a)^(2*b)))^(1/2))== 0.316;
eqn_2 = 20*log((1 + ((150/a)^(2*b)))^(1/2))==33;
sol = solve([eqn_1,eqn_2],[a,b]);
However, I could not get a returned value. I received a = a, b = b
.
Grateful for your help, and please do let me know where my mistakes are. Thank you.

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madhan ravi
madhan ravi 2018-8-21
编辑：madhan ravi 2018-8-21

0 个投票

Try this:
syms a b
eqn_1 = 20*log10((1 + ((20/a).^(2*b))).^(1/2))== 0.316;
eqn_2 = 20*log10((1 + ((150/a).^(2*b))).^(1/2))==33;
[a,b] = vpasolve([eqn_1,eqn_2],[a,b])
ANSWER
a =
33.350407439877975992438632838773
b =
2.526670930138947892001693474408
YOUR MISTAKES
1) syms f n should be syms a b
2) To view solution sol.a and sol.b you would get your answer because you received them in the form of struct so. to view struct with fields you just simply add dot in between.

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