Question

已知向量a=(-3,4)向量a平行b,且丨b丨=1,则b=

Answer 1

let b=(x,y)

a//b

-3/4 = x/y

x = (-3/4)y

|b|^2=1

x^2 +y^2 =1

(9/16)y^2 +y^2 =1

y^2 = 16/25

y = 4/5 or -4/5

b=(-3/5,4/5) or (3/5,-4/5)