Answer on Question #75326 – Math – Analytic Geometry
Question
1. Obtain the equation of the line passing through ( 1 , − 1 , 2 ) (1,-1,2) ( 1 , − 1 , 2 ) having direction ratios ( 2 , 0 , 1 ) (2,0,1) ( 2 , 0 , 1 ) .
Solution
The symmetric form of the equation of a line passing through a point M ( x 0 , y 0 , z 0 ) M(x_0, y_0, z_0) M ( x 0 , y 0 , z 0 ) and having direction ratios a a a , b b b and c c c is:
x − x 0 a = y − y 0 b = z − z 0 c \frac{x - x_0}{a} = \frac{y - y_0}{b} = \frac{z - z_0}{c} a x − x 0 = b y − y 0 = c z − z 0
The parametric form of the equation of a line passing through a point M ( x 0 , y 0 , z 0 ) M(x_0, y_0, z_0) M ( x 0 , y 0 , z 0 ) and having direction ratios a a a , b b b and c c c is:
{ x = x 0 + a t y = y 0 + b t z = z 0 + c t , t ∈ R \left\{ \begin{array}{l}
x = x_0 + a t \\
y = y_0 + b t \\
z = z_0 + c t, \quad t \in R
\end{array} \right. ⎩ ⎨ ⎧ x = x 0 + a t y = y 0 + b t z = z 0 + c t , t ∈ R
Putting the values of x 0 , y 0 , z 0 x_0, y_0, z_0 x 0 , y 0 , z 0 and a , b , c a, b, c a , b , c in (1) and (2) we get the equation of the line passing through ( 1 , − 1 , 2 ) (1,-1,2) ( 1 , − 1 , 2 ) having direction ratios ( 2 , 0 , 1 ) (2,0,1) ( 2 , 0 , 1 ) :
x − 1 2 = y + 1 0 = z − 2 1 ↔ { x = 1 + 2 t y = − 1 z = 2 + t , t ∈ R \frac{x - 1}{2} = \frac{y + 1}{0} = \frac{z - 2}{1} \leftrightarrow \left\{ \begin{array}{l}
x = 1 + 2 t \\
y = -1 \\
z = 2 + t
\end{array} \right., \qquad t \in R 2 x − 1 = 0 y + 1 = 1 z − 2 ↔ ⎩ ⎨ ⎧ x = 1 + 2 t y = − 1 z = 2 + t , t ∈ R Answer:
x − 1 2 = y + 1 0 = z − 2 1 ↔ { x = 1 + 2 t y = − 1 z = 2 + t , t ∈ R \frac{x - 1}{2} = \frac{y + 1}{0} = \frac{z - 2}{1} \leftrightarrow \left\{ \begin{array}{l}
x = 1 + 2 t \\
y = -1 \\
z = 2 + t
\end{array} \right., \qquad t \in R 2 x − 1 = 0 y + 1 = 1 z − 2 ↔ ⎩ ⎨ ⎧ x = 1 + 2 t y = − 1 z = 2 + t , t ∈ R
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