Cross-multiply: Get 0 on the right side: Use the identity So tan(x)+cot(x) must equal to any odd integer multiple of The general odd integer is 2n+1 for any integer n Take reciprocals of both sides: Multiply numerator and denominator on the right side by 2 Multiply both sides by 2 and reverse the factors on the left side to make the left side look like the right side of the identity , where n is any integer. Edwin