Subtract 2+b/ab from 3/a

Subtract 2+b/ab from 3/a

Which is an equation for the nth terms of the sequence 12,15,18,21

What are the solutions of the system? y = x^2 + 2x +3y = 4x - 2a. (-1, -6) and (-3, -14)b. (-1, 10) and (3, -6)c. no solutiond. (-1, -6) and (3, 10)

If the value of cos330°is√3/2 then find cos 165°.