Question

5. If I m and n are the direction cosines of a vector, then
a) 1 + m + n = 1
b) l² + m² + n² = 1
c) l² + m² + n² = 0
d) l + m + n =0​

Answer 1

Answer:

B). l²+m²+n² = 1

Explanation:

l = cos(a) = x/r

m = cos(b) = y/r

n = cos(c) = z/r

where r = √x²+y²+z²

where a,b,c are the angles made by the direction vector with x,y,z axes

So, l²+m²+n² = 1

Hope it helps you.