[" 91."(sin x)/(sin2x sin3x)+(sin x)/(sin3x sin4x)+(sin x)/(sin4x*sin5x)+....n],[" terms is equal to "],[[" (1) "cot2x-cot nx],[" (2) "tan2x-tan nx],[" (3) "cot2x-cot(n+2)x],[" (4) "tan(nx+3x)]]