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# Class 11-commerce RD SHARMA Solutions Maths Chapter 28 - Introduction to 3-D coordinate geometry

## Introduction to 3-D coordinate geometry Exercise Ex. 28.1

### Solution 1(i)

All are positive, so octant is XOYZ

### Solution 1(ii)

X is negative and rest are positive, so octant is X'OYZ

### Solution 1(iii)

Y is negative and rest are positive, so octant is XOY'Z

### Solution 1(iv)

Z is negative and rest are positive, so octant is XOYZ'

### Solution 1(v)

X and Y are negative and Z is positive, so octant is X'OY'Z

### Solution 1(vi)

All are negative, so octant is X'OY'Z'

### Solution 1(vii)

Y and Z are negative, so octant is XOY'Z'

### Solution 1(viii)

X and Z are negative, so octant is X'OYZ'

### Solution 2(i)

YZ plane is x-axis, so sign of x will be changed. So answer is (2, 3, 4)

### Solution 2(ii)

XZ plane is y-axis, so sign of y will be changed. So answer is (-5, -4, -3)

### Solution 2(iii)

XY-plane is z-axis, so sign of Z will change. So answer is (5, 2, 7)

### Solution 2(iv)

XZ plane is y-axis, so sign of Y will change, So answer is (-5, 0, 3)

### Solution 2(v)

XY plane is Z-axis, so sign of Z will change So answer is (-4, 0, 0)

### Solution 3

Vertices of cube are

(1, 0, -1) (1, 0, 4) (1, -5, -1)

(1, -5, 4) (-4, 0, -1) (-4, -5, -4)

(-4, -5, -1) (4, 0, 4) (1, 0, 4)

### Solution 4

3-(-2)=5, |0-5|=5, |-1-4|=5

5, 5, 5 are lengths of edges

### Solution 5

5-3=2, 0-(-2)=2, 5-2=3

2, 2, 3 are lengths of edges

### Solution 7

(-3, -2, -5) (-3, -2, 5) (3, -2, -5) (-3, 2, -5) (3, 2, 5)

(3, 2, -5) (-3, 2, 5)