i dont know why there is no anwser about this 'solve'

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cehua liu
cehua liu 2023-3-8
编辑： Torsten 2023-3-9
clc;
close all;
clear;
a1=20;
b1=20;
k1=sqrt((a1+10)^2+b1^2)-sqrt((a1-10)^2+b1^2)
syms a b k;
equ2= a==20;
equ3= b==20;
equ1= k==sqrt((a+10)^2+b^2)-sqrt((a-10)^2+b^2);
k=solve(equ1,equ2,equ3,k)

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Fabio Freschi
Fabio Freschi 2023-3-8
编辑：Fabio Freschi 2023-3-8
Ran in:
Your call to solve is incorrect
clear all
syms a b k
equ2= a==20;
equ3= b==20;
equ1= k==sqrt((a+10)^2+b^2)-sqrt((a-10)^2+b^2);
sol=solve([equ1; equ2; equ3],[k a b])
sol = struct with fields:
k: 1300^(1/2) - 500^(1/2) a: 20 b: 20

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Torsten
Torsten 2023-3-8
编辑：Torsten 2023-3-8
Ran in:
Three equations need three unknowns, not only one.
clc;
close all;
clear;
a1=20;
b1=20;
k1=sqrt((a1+10)^2+b1^2)-sqrt((a1-10)^2+b1^2)
k1 = 13.6948
syms a b k
equ2= a==20;
equ3= b==20;
equ1= k==sqrt((a+10)^2+b^2)-sqrt((a-10)^2+b^2);
sol=solve([equ1,equ2,equ3],[a b k])
sol = struct with fields:
a: 20 b: 20 k: 1300^(1/2) - 500^(1/2)
k = double(sol.k)
k = 13.6948
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cehua liu
cehua liu 2023-3-8
clc;
close all;
clear;
syms a b;
equ1= sqrt((a+10)^2+b^2)-sqrt((a-10)^2+b^2)==sqrt((20+10)^2+20^2)-sqrt((20-10)^2+20^2);%a=b=20
equ2= a>=0;
equ3= b>=0;
sol=solve([equ1;equ2;equ3],[a b]);
a=sol.a
sir,i am sorry.if i have only tow unknowns,but three equations are needed.，What should we do in this case.
Then why can't the above code run correctly? Isn't there a clear result of 20
Torsten
Torsten 2023-3-9
编辑：Torsten 2023-3-9
Ran in:
All the points on the blue curve below are solutions. MATLAB cannot list all of them - thus it lists none.
hold on
fimplicit(@(a,b)sqrt((a+10).^2+b.^2)-sqrt((a-10).^2+b.^2)-(sqrt((20+10)^2+20^2)-sqrt((20-10)^2+20^2)),[0 40 0 40])
plot(20,20,'o')
hold off
grid on

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