第 12 类 RD Sharma 解决方案 - 第 29 章飞机 - 练习 29.15 |设置 2
问题 8. 求平面 2x – y + z + 3 = 0 中点 (1, 3, 4) 的图像。
解决方案:
According to the question we have to find the image of point P(1, 3, 4)
in the plane 2x – y + z +3 = 0
Now let us assume that Q be the image of the point.
Here, the direction ratios of normal to plane = 2, -1, 1
The direction ratios of PQ which is parallel to the normal to the plane
is proportional to 2, -1, 1 and the line PQ is passing through point P(1, 3, 4).
Thus, equation of the line PQ is:
Now, the general point on the line PQ = (2λ + 1, -λ + 3, λ + 4)
Let Q = (2λ + 1, -λ + 3, λ + 4) -Equation(1)
Here, Q is the image of P, so R is the mid point of PQ
Coordinates of R =
Point R is lies on the plane 2x – y + z + 3 = 0
= 2(λ + 1) –
4λ + 4 + λ – 6 + λ + 8 + 6 = 0
6λ = -12
λ = -2
Now, put the value of λ in equation(1), we get
= (-4 + 1, 2 + 3, -2 + 4)
= (-3, 5, 2)
Hence, the image of point P(1, 3, 4) is (-3, 5, 2)
问题9.用位置向量求点的距离从线的交点与飞机 .
解决方案:
According to the question we have to find distance of a point A with position
vector from the point of intersection of
line
with plane
Let the point of intersection of line and plan be
The line and the plane will intersect when,
(2 + 3λ)(1) + (-1 + 4λ)(-1) + (2 + 12λ)(1) = 5
2 + 3λ + 1 – 4λ + 2 + 12λ = 5
11λ = 5 – 5
λ = 0
So, the point B is given by
The required distance is 13 units.
问题 10. 求点 (1, 1, 2) 到平面的垂线的长度和底 .
解决方案:
Plane = x – 2y + 4z + 5 = 0 -Equation(1)
Point = (1, 1, 2)
D =
= 12/√21
The length of the perpendicular from the given point to the plane = 12/√21
Let us assume that the foot of perpendicular be (x, y, z).
So DR’s are in proportional
x = k + 1
y = -2k + 1
z = 4k + 2
Substitute (x, y, z) = (k + 1, -2k + 1, 4k + 2) in the plane equation(1)
k + 1 + 4k – 2 + 16k + 8 + 5 = 0
21k = -12
k = -12/21 = -4/7
Hence, the coordinate of the foot of the perpendicular = (3/7, 15/7, -2/7)
问题 11. 求垂线脚的坐标和点 P(3, 2, 1) 到平面 2x – y + z + 1 = 0 的垂线距离。同时求该点在平面上的像.
解决方案:
Given:
Plane = 2x – y + z + 1 = 0 -Equation(1)
Point P = (3, 2, 1)
D =
The perpendicular distance of the point P from the plane(D) = √6
Let us assume that the foot of perpendicular be (x, y, z).
So DR’s are in proportional
x = 2k + 3
y = -k + 2
z = k + 1
Substitute (x, y, z) = (2k + 3, -k + 2, k + 1) in the plane equation(1)
4k + 6 + k – 2 + k + 1 + 1 = 0
6k = -6
k = -6/6 = -1
The coordinate of the foot of the perpendicular = (1, 3, 0)
问题12.求垂直于平面的单位向量的方向余弦穿越原点。
解决方案:
Given:
Equation of the plane
Thus, the direction ratios normal to the plane are 6, -3 and -2
Hence, the direction cosines to the normal to the plane are
=
= 6/7, -3/7, -2/7
= -6/7, 3/7, 2/7
The direction cosines of the unit vector perpendicular to the plane
are same as the direction cosines of the unit vector perpendicular
to the plane are: -6/7, 3/7, 2/7
问题 13. 求从原点到平面 2x – 3y + 4z – 6 = 0 的垂线的底坐标。
解决方案:
According to the question,
Plane = 2x – 3y + 4z – 6 = 0
The direction ratios of the normal to the plane are 2, -3 and 4.
Thus, the direction ratios of the line perpendicular to the plane are 2, -3 and 4.
The equation of the line passing (x1, y1, z1) having direction ratios a, b and c is
Thus, the equation of the line passing through the origin
with direction ratios 2, -3 and 4 is
Here, r is same constant.
Any point on the line is of the form 2r, -3r, and 4r,
if the point P(2r, -3r, 4r) lies on the plane 2x – 3y + 4z – 6 = 0.
Thus, we have,
2(2r) – 3(-3r) + 4(4r) – 6 = 0
4r + 9r + 16r – 6 = 0
29r = 6
r = 6/29
Thus, the coordinates of the point of intersection of the perpendicular
from the origin and the plane are:
P(2×6/29, -3×629, 4×6/29) = P(12/29, -18/29, 24/29)
问题 14. 求点 (1, 3/2, 2) 到平面 2x – 2y + 4z +5 = 0 的垂线的长度和底。
解决方案:
Given:
Point = (1, 3/2, 2)
Plane = 2x – 2y + 4z + 5 = 0
D =
= √6
So, the length of the perpendicular from the point to the plane(D) = √6
Let the foot of perpendicular be (x, y, z). So, DR’s are in proportional
x = 2k + 1
y = -2k + 3/2
z = 4k + 2
So, using the values of x, y, z in equation of the plane we have,
2(2k + 1) – 2(-2k + 2/3) +4(4k + 2) + 5 = 0
4k + 2 + 4k – 3 + 16k + 8 + 5 = 0
24k = -12
k = -1/2
So, the coordinate of the foot of the perpendicular = (0, 5/2, 0)