Orienting Yourself: The Use of Coordinates | Exercise 1.2

Question 4

Other rooms in the house:

(i) Reiaan’s room door leads from the dining room which has the length 18 ft and width 15 ft. The length of the dining room extends from point P to point A. Sketch the dining room and mark the coordinates of its corners.

(ii) Place a rectangular 5 ft × 3 ft dining table precisely in the centre of the dining room. Write down the coordinates of the feet of the table.

Question diagram 1
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Solution

We will use the given coordinates and dimensions to find the dining room and table coordinates.

Step 1 — Dining Room Corners

Let's find the coordinates of points P and A from the diagram. Point P is at (-6, 0). Point A is at (12, 0). The length of the dining room is given as 18 ft. Let's check this length using the coordinates.

PA length=xAxPPA \text{ length} = x_A - x_P

=12(6)= 12 - (-6)

=12+6= 12 + 6

18 ft\boxed{18 \text{ ft}}

This matches the given length. The dining room is 15 ft wide. It lies below the line segment PA. So, its y-coordinates will be negative. The y-coordinate of P and A is 0. The bottom corners will have a y-coordinate of 015=15\mathbf{0 - 15 = -15}. Let's name the other two corners Q and S. Point Q will be directly below A. Point S will be directly below P. The coordinates of Q are (12, -15). The coordinates of S are (-6, -15).

Diagram 1

Step 2 — Dining Table Coordinates

First, we find the center of the dining room. The x-coordinates range from -6 to 12. The y-coordinates range from 0 to -15.

x-coordinate of center=6+122x\text{-coordinate of center} = \frac{-6 + 12}{2}

=62= \frac{6}{2}

=3= 3

y-coordinate of center=0+(15)2y\text{-coordinate of center} = \frac{0 + (-15)}{2}

=152= \frac{-15}{2}

=7.5= -7.5

The center of the dining room is at (3, -7.5). The dining table is 5 ft × 3 ft. Let's assume the length is along the x-axis and width along the y-axis. Half of the length is 5/2=2.5\mathbf{5/2 = 2.5} ft. Half of the width is 3/2=1.5\mathbf{3/2 = 1.5} ft. Now we find the coordinates of the table's feet. These are the four corners of the table.

xleft=32.5=0.5x_{\text{left}} = 3 - 2.5 = 0.5

xright=3+2.5=5.5x_{\text{right}} = 3 + 2.5 = 5.5

ybottom=7.51.5=9y_{\text{bottom}} = -7.5 - 1.5 = -9

ytop=7.5+1.5=6y_{\text{top}} = -7.5 + 1.5 = -6

The four corners are: (x_left, y_bottom) = (0.5, -9) (x_right, y_bottom) = (5.5, -9) (x_right, y_top) = (5.5, -6) (x_left, y_top) = (0.5, -6)

Diagram 2

Answer

(i) The coordinates of the dining room corners are: (-6, 0), (12, 0), (12, -15), (-6, -15). (ii) The coordinates of the four feet of the dining table are: (0.5, -9), (5.5, -9), (5.5, -6), (0.5, -6).

More questions in Exercise 1.2

Q1

Place Reiaan’s rectangular study table with three of its feet at the points (8, 9), (11, 9) and (11, 7).

(i) Where will the fourth foot of the table be? (ii) Is this a good spot for the table? (iii) What is the width of the table? The length? Can you make out the height of the table?

Q2

If the bathroom door has a hinge at B1\text{B}_1 and opens into the bedroom, will it hit the wardrobe? Are there any changes you would suggest if the door is made wider?

Q3

Look at Reiaan’s bathroom.

(i) What are the coordinates of the four corners O, F, R, and P of the bathroom?

(ii) What is the shape of the showering area SHWR in Reiaan’s bathroom? Write the coordinates of the four corners.

(iii) Mark off a 3 ft × 2 ft space for the washbasin and a 2 ft × 3 ft space for the toilet. Write the coordinates of the corners of these spaces.

Q4

Other rooms in the house:

(i) Reiaan’s room door leads from the dining room which has the length 18 ft and width 15 ft. The length of the dining room extends from point P to point A. Sketch the dining room and mark the coordinates of its corners.

(ii) Place a rectangular 5 ft × 3 ft dining table precisely in the centre of the dining room. Write down the coordinates of the feet of the table.

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