let b=(x,y,z) be the vector
垂直于X轴
=> x =0 (1)
垂直于向量a=2j+5j+k
a.b =0
(2j+5j+k).(x+y+z) =0
2x+5y+z=0
5y+z =0 (2)
单位向量
=> x^2+y^2+z^2 =1
y^2 + z^2 =1
y^2+25y^2=1
y = √26/26 or -√26/26
y = √26/26 ,z= -5√26/26
y = -√26/26 ,z= 5√26/26
单位向量 b
=(0,√26/26 ,-5√26/26) or (0,-√26/26 ,5√26/26)