Question:

The cartesian equation of a line is \(\frac{x-5}{3}=\frac{y+4}{7}=\frac{z-6}{2}\). Write its vector form.

Updated On: Sep 20, 2023
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Solution and Explanation

The Cartesian equation of the line is \(\frac{x-5}{3}=\frac{y+4}{7}=\frac{z-6}{2}\)……….....(1)
The given line passes through the point (5,-4,6).
The position vector of this point is \(\vec a = 5\hat i-4\hat j +6 \hat k\)
Also, the direction ratios of the given line are 3, 7, and 2.

This means that the line is in the direction of the vector, \(\vec b\)=3\(\hat i\)+7\(\hat j\)+2\(\hat k\)

It is known that the line through position vector \(\vec a\) and in the direction of the vector \(\vec b\) is given by the equation,
\(\vec r\)=\(\vec a\)\(\vec b\), λ∈R
⇒ \(\vec r\)=(5\(\vec i\)-4\(\vec j\)+6\(\vec k\))+λ(3\(\vec i\)+7\(\vec j\)+2\(\vec k\))

This is the required equation of the given line in vector form.

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Concepts Used:

Equation of a Line in Space

In a plane, the equation of a line is given by the popular equation y = m x + C. Let's look at how the equation of a line is written in vector form and Cartesian form.

Vector Equation

Consider a line that passes through a given point, say ‘A’, and the line is parallel to a given vector '\(\vec{b}\)‘. Here, the line ’l' is given to pass through ‘A’, whose position vector is given by '\(\vec{a}\)‘.  Now, consider another arbitrary point ’P' on the given line, where the position vector of 'P' is given by '\(\vec{r}\)'.

\(\vec{AP}\)=𝜆\(\vec{b}\)

Also, we can write vector AP in the following manner:

\(\vec{AP}\)=\(\vec{OP}\)\(\vec{OA}\)

𝜆\(\vec{b}\) =\(\vec{r}\)\(\vec{a}\)

\(\vec{a}\)=\(\vec{a}\)+𝜆\(\vec{b}\)

\(\vec{b}\)=𝑏1\(\hat{i}\)+𝑏2\(\hat{j}\) +𝑏3\(\hat{k}\)