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    				| 1. | A vector ` vec r`is inclinedat equal acute angles of `x-a xi s ,``y-a xi s`and `z-a xi sdot`if `| vec r|=6`units, find ` vec rdot` | 
| Answer» As the given line is equally inclined with all three coordinate axis, let it create angle `alpha` with all three coordinate axis. Then, Direction cosines will be `(cos alpha,cos alpha,cos alpha)`. `:. cos^2alpha+cos^2alpha+cos^2alpha = 1` `=>3cos^2alpha = 1` `=>cos alpha = +-1/sqrt3` Since `vecr` is inclined at acute angle, therefore, `cos alpha = 1/sqrt3`. Direction cosines will be `(1/sqrt3,1/sqrt3,1/sqrt3)`. Now, `|vecr| = 6` Therefore, `vecr = |vecr|(lhati+mhatj+nhatk) ` `vecr = 6(1/sqrt3hati+1/sqrt3hatj+1/sqrt3hatk) ` `vecr = 2sqrt3(hati+hatj+hatk) .` | |