General solution of simultaneous equations tanθ=−13 and cosθ=32 is
θ=nπ+π6,n∈z
θ=nπ+11π6,n∈z
θ=2nπ+π3,n∈z
θ=2nπ+11π6,n∈z
We have tanθ=−13<0,cosθ=32>0
∴θbelongs to 4th quadrant and it is 2π−π6=11π6
∴general solution is θ=2nπ+11π6,n∈z