Homework Statement
A vector r has length 21 and direction ratio's 2,-3,6. The direction cosines of r, given that r makes an obtuse angle with x-axis is given by?
Homework Equations
l/a = m/b =n/c ...(1) (l,m,n are direction cosines, a,b,c are direction ratios
l^2 + m^2 + n^2=1...(2)
The...