A city planner is designing a straight road connecting a School located at S(1, 7) and a Hospital located at H(7, –5). A Bus Stop B is to be placed on this road such that SB : BH = 1 : 2. A Fire Station F is to be placed at the point that divides segment SH in the ratio 2 : 1.
A city planner is designing a straight road connecting a School located at S(1, 7) and a Hospital located at H(7, –5). A Bus Stop B is to be placed on this road such that SB : BH = 1 : 2. A Fire Station F is to be placed at the point that divides segment SH in the ratio 2 : 1.
(i) Find the coordinates of the Bus Stop B.
(ii) Find the coordinates of the Fire Station F.
(iii) The city planner claims that the midpoint M of segment SH, the Bus Stop B, and the Fire Station F are NOT collinear. Verify whether the claim is correct, showing full working.
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S(1, 7), H(7, –5), ratio m : n = 1 : 2
Using the Section Formula:
B = ( (m·x₂ + n·x₁)/(m + n) , (m·y₂ + n·y₁)/(m + n) )
⟹ B = ( (1×7 + 2×1)/(1 + 2) , (1×(–5) + 2×7)/(1 + 2) )
⟹ B = ( (7 + 2)/3 , (–5 + 14)/3 )
⟹ B = ( 9/3 , 9/3 )
∴ Coordinates of Bus Stop B = (3, 3)
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(ii) Finding coordinates of Fire Station F [1 mark]
S(1, 7), H(7, –5), ratio m : n = 2 : 1
Using the Section Formula:
F = ( (2×7 + 1×1)/(2 + 1) , (2×(–5) + 1×7)/(2 + 1) )
⟹ F = ( (14 + 1)/3 , (–10 + 7)/3 )
⟹ F = ( 15/3 , –3/3 )
∴ Coordinates of Fire Station F = (5, –1)
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(iii) Verifying whether M, B, F are collinear [2 marks]
First, find midpoint M of SH:
Using the Midpoint Formula:
M = ( (x₁ + x₂)/2 , (y₁ + y₂)/2 )
⟹ M = ( (1 + 7)/2 , (7 + (–5))/2 )
⟹ M = ( 8/2 , 2/2 )
∴ M = (4, 1)
Now check collinearity of M(4, 1), B(3, 3), F(5, –1) using the Area of Triangle formula:
Area = ½ |x₁(y₂ – y₃) + x₂(y₃ – y₁) + x₃(y₁ – y₂)|
Here (x₁, y₁) = M(4, 1), (x₂, y₂) = B(3, 3), (x₃, y₃) = F(5, –1)
⟹ Area = ½ |4(3 – (–1)) + 3((–1) – 1) + 5(1 – 3)|
⟹ Area = ½ |4(4) + 3(–2) + 5(–2)|
⟹ Area = ½ |16 – 6 – 10|
⟹ Area = ½ |0|
⟹ Area = 0
∵ Area of triangle formed by M, B, F = 0, the three points are collinear.
∴ The city planner's claim is INCORRECT. M, B, and F all lie on segment SH itself and are therefore collinear.