this is a question from chhaya prakasani sn dey please solve it

Im writing theta as x .Write tan(120+x)= -cot(x+30). Now find value of m/n which comes out to be -cot(x+30)/tan(x-30). Now in m+n/m-n divide by n to get ((m/n)+1)/((m/n)-1). Now put value of m/n and express tan and cot in form of sin and cos, and use formula of cos(A+B) and cos(A-B) to get answer as 2cos2x.Feel free to ask any doubt regarding it.