How to solve an equation equal to zero?
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Hello,
I want to solve this equation equal to zero to find the theta, But it doesn't give me an answer there is an error. How to do it, thanks for the help.
eqn=sind(45)*sind(45+thtea)+sind(45+thtea)*sind(45+thtea)+cosd(45)*cos(45+thtea)+cosd(45+thtea)*cosd(45+thtea)==0
eqn=sind(45)*sind(45+thtea)+sind(45+thtea)*sind(45+thtea)+cosd(45)*cos(45+thtea)+cosd(45+thtea)*cosd(45+thtea)
solve(eqn,thtea)
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Accepted Answer
Walter Roberson
on 28 Jul 2022
There are at least 84 solutions, possibly more. Are you expecting to get a closed form solution that lists each of the angles that satisfies the equation? Because that is not going to happen -- trig equations seldom have closed form solutions.
Notice that your cos^2 and sin^2 add up to 1.
And notice that you have cos(45+thtea) instead of cosd(45+thtea) at one point.
syms thtea real
eqn=sind(45)*sind(45+thtea)+sind(45+thtea)*sind(45+thtea)+cosd(45)*cos(45+thtea)+cosd(45+thtea)*cosd(45+thtea)==0
simplify(eqn)
solve(eqn)
vpasolve(eqn)
fplot([lhs(eqn)-rhs(eqn),0], [-360, 360])
fplot([lhs(eqn)-rhs(eqn),0], [-225, -70])
eqn2 = sind(45)*sind(45+thtea)+sind(45+thtea)*sind(45+thtea)+cosd(45)*cosd(45+thtea)+cosd(45+thtea)*cosd(45+thtea)==0
eqn2 = simplify(eqn2)
sol2 = solve(eqn2, 'returnconditions', true)
sol2.thtea
sol2.conditions
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