Manipal Entrance Test 2019 Math Paper

Let α,β,γ be the angles which the line makes with the positive directions at the axes of x,y and z respectively, then cos‌α,cos‌β and cos‌γ are called the direction cosines of the line and these are usually denoted by
l=cos‌α,m=cos‌β,n=cos‌γ
∴cos2α+cos2β+cos2γ =l2+m2+n2=1