`5x-3=15y+7=3-10z`
`5(x-3/5)=15(y+7/5)=-10(z-3/10)`
`(x-3/5)/(1/5)=(y+7/15)/(1/15)=(z-3/10)/(-1/10)`
`l:m:n=1/5:1/15:-1/10=6:2:-3`
`sqrt(l^2+m^2+n^2)=sqrt(6^2+2^2+3^2)=7`
`cosalpha=6/7,alpha=cos^(-1)(6/7)`
`cosbeta-2/7=beta=cos^(-1)(2/7)`
`cosgamma=-3/7=gamma=cos^(-1)(-3/7)`
`=(6/7,2/7,-3/7)`.
