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Three Dimensional Geometry

Short Answer Type

171. Find the equation of the plane which is parallel to the x-axis and has intercepts 5 and 7 on the y and z-axis, respectively.

Let the equation of plane be

straight x over straight a plus straight y over straight b plus straight z over straight c equals 1

...(1)
Here b = 5, c = 7 ...(2)
Since the plane is parallel to x-axis whose direction ratios are 1, 0, 0
∴ normal to the plane must be perpendicular to the x-axis. But the direction ratios of the normal to the plane are

1 over straight a comma space 1 over straight b comma space 1 over straight c.

therefore space space space space 1 over straight a cross times 1 plus space 1 over straight b cross times 0 space plus space 1 over straight c cross times 0 space equals space 0 space space space space space space space rightwards double arrow space space space space space 1 over straight a space equals space 0

...(3)
From (1) and (2), (3), we have

straight y over 5 plus straight z over 7 space equals space 1 space space space space or space space 7 straight y space plus space 5 straight z space equals space 35

which is required equation of plane.

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172. Find the D.C.’s of the perpendicular from origin to the plane

straight r with rightwards arrow on top. space open parentheses negative 2 space straight i with hat on top space minus space 3 space straight j with hat on top space plus space 6 space straight k with hat on top close parentheses plus 14 space equals space 0.

Find also the distance of the plane from the origin.

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Long Answer Type

173. A plane meets the coordinate axes in A, B, C and (α, β, γ) is the centroid of the triangle ABC. Then, show that the equation of the plane is

straight x over straight alpha plus straight y over straight beta plus straight z over straight gamma space equals space 3.

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Short Answer Type

174. A plane meets the co-ordinate axes at A, B, C such that the centroid of the triangle ABC is the point (1, – 2, 3). Show that the equation of the plane is 6x-3y + 2z= 18.

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Long Answer Type

175. A plane meets the co-ordinate axes at A, B, C such that the centroid of triangle ABC is the point (a, b, c). Show that the equation of the plane is

straight x over straight a plus straight y over straight b plus straight z over straight c equals 3.

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Short Answer Type

176. Find the vector equation of the following planes in scalar product form:

straight r with rightwards arrow on top space equals space straight i with hat on top space minus space straight j with hat on top space plus space straight lambda open parentheses straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top close parentheses space plus space straight mu space open parentheses straight i with hat on top space minus space 2 space straight j with hat on top space plus space 3 space straight k with hat on top close parentheses

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177. Find the vector equation of the following planes in scalar product form:

straight r with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space straight k with hat on top space plus space straight lambda space straight i with hat on top space plus space straight mu space open parentheses straight i with hat on top space minus space 2 space space straight j with hat on top space minus space straight k with hat on top close parentheses

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Long Answer Type

178. Find the vector equation of the plane in scalar product form

straight r with rightwards arrow on top space equals space straight i with hat on top space minus space straight j with hat on top space plus space straight lambda space open parentheses straight i with hat on top space plus space straight j with hat on top space plus space straight k with hat on top close parentheses space plus space straight mu space open parentheses 4 straight i with hat on top space minus space 2 space straight j with hat on top space plus space 3 space straight k with hat on top close parentheses.

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179.

Find the vector equation in scalar product form of the plane that contains the lines.
$straight r with rightwards arrow on top space equals space left parenthesis straight i with hat on top space plus space straight j with hat on top right parenthesis space plus space straight s space left parenthesis straight i with hat on top space plus 2 space straight j with hat on top space minus space straight k with hat on top right parenthesis$
and $straight r with rightwards arrow on top space equals space open parentheses straight i with hat on top plus straight j with hat on top close parentheses plus straight t open parentheses negative straight i with hat on top space plus space straight j with hat on top space minus space 2 space straight k with hat on top close parentheses$

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Short Answer Type

180. Find the vector equation of the straight line passing through (1, 2, 3) and perpendicular to the plane

straight r with rightwards arrow on top. space open parentheses straight i with hat on top space plus space 2 space straight j with hat on top space minus space 5 space straight k with hat on top close parentheses space plus space 9 space equals 0 space

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