1. The problem statement, all variables and given/known data Can you plz list the formulae of function change while putting (pie/2 - x) and adding or subtracting 2Pie Basicly, I need help on 2 formulae. One is add/subtract Pie/2 and the other is add/subtract 2Pie. 2. Relevant equations sin (pie/2 - x) = sin x cos (pie/2 - x) = - sin x sin (2Pie - x) = -cos x something like that.... Its just example, may not be correct. 3. The attempt at a solution I know a little something that All is +ve in first quadrant, only sin is +ve in 2nd quad, tan in 3rd and cos in 4th quad. Maybe we can use this to determine +ve or -ve sin/cos when we add or subtract 2Pie or Pie.