1）向量a = (2- -2, 1-4) = (4, -3)|a| = √(4^2 + (-3)^2) = 52)设单位向量为b=（cosb, sinb）ab = 4cosb - 3sinb = 0 所以 cosb = 3/5或者 -3/5sinb =4/5或者-4/5即单位向量为（3/5, ...