Lettheunitvector→a=xˆi+yˆj+zˆk|a|=1=x2+y2+z2−−−−(i)Now,Let→b=2ˆi−ˆj+ˆk→c=3ˆi−4ˆj−ˆkA/q→a.→b=(xˆi+yˆj+zˆk)(2ˆi−ˆj+ˆk)2x−y+z=0−−−−(ii)and,→a.→c=(xˆi+yˆj+zˆk)(3ˆi−4ˆj−ˆk)3x−4y−z=0−−−−(iii)Onsolvingequn(ii)and(iii)wegetx=1√3,y=1√3z=−1√3requiredvector=1√3(ˆi+ˆj−ˆk)