1. The problem statement, all variables and given/known data if a =3i-4j find a unit vector perpendicular a 2. Relevant equations Vector 3. The attempt at a solution <a> = <3 , -4> <n> = <x, y> : x² + y² = 1 <a>•<n> = 3x-4y = 0 y = (3/4)x x² + (9/16)x² = 1 25x² = 16 x = -4/5, 4/5 y = -3/5, 3/5 There are two unit vectors normal to a which have opposite directions: n =(4i + 3j)/5 and n = -(4i+3j)/5 This is the answer that given by my textbook. Can somebody explain to me the 2nd step <n> = <x, y> : x² + y² = 1 I do not understand why it use x^2+y^2=1 as this is circle equation.