J & K CET Engineering J and K - CET Engineering Solved Paper-2010

  • question_answer
    The vector equation of the straight line \[6x-8=2y-7=3z\]is

    A)  \[\vec{r}=\left( \frac{8}{6}\hat{i}+\frac{7}{2}\hat{j} \right)+t\left( \frac{1}{6}\hat{i}+\frac{1}{2}\hat{j}-\frac{1}{3}\hat{k} \right)\]

    B)  \[\vec{r}=\left( \frac{8}{6}\hat{i}+\frac{7}{2}\hat{j} \right)+s\left( \frac{1}{6}\hat{i}+\frac{1}{2}\hat{j}-\frac{1}{3}\hat{k} \right)\]

    C)  \[\vec{r}=\left( -\frac{8}{6}\hat{i}-\frac{7}{2}\hat{j} \right)+t\left( \frac{1}{6}\hat{i}+\frac{1}{2}\hat{j}-\frac{1}{3}\hat{k} \right)\]

    D)  \[\vec{r}=\left( -\frac{8}{6}\hat{i}-\frac{7}{2}\hat{j} \right)+s\left( \frac{1}{6}\hat{i}-\frac{1}{2}\hat{j}-\frac{1}{3}\hat{k} \right)\]

    Correct Answer: B

    Solution :

    Given, equation of straight line is \[6x-8=2y-7=3z\] \[\Rightarrow \] \[6\left( x-\frac{8}{6} \right)=2\left( y-\frac{7}{2} \right)=3\,(z-0)\] \[\Rightarrow \] \[\frac{x-\frac{8}{6}}{\frac{1}{6}}=\frac{y-\frac{7}{2}}{\frac{1}{2}}=\frac{z-0}{1/3}\] Vector equation of this straight line is \[\vec{r}=\left( \frac{8}{6}\hat{i}+\frac{7}{2}\hat{j}+0\hat{k} \right)+s\left( \frac{1}{6}\hat{i}+\frac{1}{2}\hat{j}+\frac{1}{3}\hat{k} \right)\] \[\vec{r}=\left( \frac{8}{6}\hat{i}+\frac{7}{2}\hat{j} \right)+s\left( \frac{1}{6}\hat{i}+\frac{1}{2}\hat{j}+\frac{1}{3}\hat{k} \right)\]


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