Solve equation with 2 unknowns using solve
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How to solve the two equation below?
cos(3a)+cos(3b)=0
cos(a)+cos(b)=1.6
Ans:
a = 7.6 degree = 0.132645 rad
b = 52.4 degree = 0.9145525 rad
Hereby my code
syms a b
sol = solve(cos(3*a)+cos(3*b)==0, cos(a)+cos(b)==1.6,[a,b])
sol.a
sol.b
and it gave me this
In sym/solve>warnIfParams (line 478)
In sym/solve (line 357)
sol =
struct with fields:
a: [1×1 sym]
b: [1×1 sym]
ans =
z
ans =
z1
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채택된 답변
Walter Roberson
2021년 6월 30일
syms a b
sol = vpasolve(cos(3*a)+cos(3*b)==0, cos(a)+cos(b)==1.6,[a,b],[0, pi; 0, pi])
sol.a
sol.b
Your equations are symmetric in your variables, so this is an equivalent solution to what you posted.
추가 답변 (1개)
Alan Stevens
2021년 6월 30일
There are an infinite number of solutions! Restrict the range. One possibility is as follows
bfn = @(a) acos(1.6-cos(a));
fn = @(a) cos(3*a)+cos(3*bfn(a));
a0 = 0.1; % initial guess
a = fzero(fn, a0);
b = bfn(a);
disp([a, b])
disp(rad2deg([a,b]))
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