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Show that the lines ` vec r=( hat i+ hat j- hat k)+lambda(3 hat i- hat j)a n d vec r=(4 hat i- hat k)+mu(2 hat i+3 hat k)`are coplanar. Also, find the plane containing these two lines. |
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Answer» The given lines are `vec(r ) =(hat(i) +hat(j) -hat(k)) +lambda (3hat(i) -hat(j))` `vec( r) =(4hat(i) -hat(k)) +mu (2hat(i) +3hat(k))` These lines will intersect if for some particular values of `lambda " and " mu` the values `vec( r) ` given by (1) and (2) are the same So, we must have `(hat(i) +hat(j)-hat(k))+lambda(3hat(i)-hat(j))=(4hat(i)-hat(k))+mu(2hat(i)+3hat(k))` `rArr (1+3lambda)hat(i) +(1-lambda)hat(j) -hat(k)=(4+2mu) hat(i) +(3mu-1)hat(k)` `rArr 1+3lambda =4+2mu,1 -lambda =0 " and " 3mu-1 =-1` `rArr 3lambda -2mu =3 .....(i),lambda , =1 ...(i) " and " mu =0 .....(iii)` Clearly `lambda=1 " and " mu =0` also satisfy (i) Hence the given lines intersect . Putting `lambda =1 " in (1) we get " vec(r ) =(4hat(i) +0hat(j) -hat(k))` Hence the point of intersection of the given lines is (4,0 ,-1 ) |
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