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

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)

Answer 1

[Fabio Freschi]

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

[cehua liu]

thank you!!!!!!!!!!

Answer 2

[Torsten]

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

[cehua liu]

thank you!!!!!!!!!!!!!

[cehua liu]

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]

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