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NCERT Class XII Mathematics Chapter - - Solutions

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Question : 77 of 78
Marks: +1, -0
Find the distance of the point ( – 1, – 5, – 10) from the point of intersection of the line r=2i^j^+2k^\vec{r}=2\hat{i}-\hat{j}+2\hat{k} +λ(3i^+4j^+2k^)+\lambda(3\hat{i}+4\hat{j}+2\hat{k}) and the plane r(i^j^+k^)=5\vec{r}\cdot(\hat{i}-\hat{j}+\hat{k})=5.
Solution:  
The given line is r=2i^j^+2k^\vec{r}=2\hat{i}-\hat{j}+2\hat{k} +λ(3i^+4j^+2k^)+\lambda(3\hat{i}+4\hat{j}+2\hat{k}) ...(1)
and the given plane is r(i^j^+k^)=5\vec{r}\cdot(\hat{i}-\hat{j}+\hat{k})=5...(2)
Solving (1) and (2), we get
(2+3λ)(1)+(4λ1)(1)+(2λ+2)(1)=5(2+3\lambda)(1)+(4\lambda-1)(-1)+(2\lambda+2)(1)=5
2+3λ4λ+1+2λ+2=5\Rightarrow 2+3\lambda-4\lambda+1+2\lambda+2=5
λ=0\Rightarrow \lambda=0
∴ The point of intersection of (1) and (2) is
(2i^j^+2k^)(2\hat{i}-\hat{j}+2\hat{k}) i.e., (2 1− 2)
The other point is (–1, –5, –10).
∴ Required distance =(12)2+(5+1)2+(102)2=13=\sqrt{(-1-2)^2+(-5+1)^2+(-10-2)^2}=13
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