设a0(x,y)
因为 a b垂直
=> a.b =0
(x,y).(3,4) =0
3x+4y=0
|a0|=1(单位向量)
=>x^2+y^2=1
x^2 + 9x^2 /16 =1
25x^2/16 =1
x = 4/5 or-4/5
when x =4/5, y = -3/5
when x =-4/5, y = 3/5
a0= (4/5, -3/5) or (-4/5, 3/5)