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Complete the following theorem: If a line divides two sides of a triangle in the same proportion, then the line is .. - NSC Technical Mathematics - Question 9 - 2019 - Paper 2

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Complete the following theorem: If a line divides two sides of a triangle in the same proportion, then the line is ... The diagram below shows circle DGF with cent... show full transcript

Worked Solution & Example Answer:Complete the following theorem: If a line divides two sides of a triangle in the same proportion, then the line is .. - NSC Technical Mathematics - Question 9 - 2019 - Paper 2

Step 1

Show, with reasons, that DF || BC.

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Answer

Since OG ⊥ DF and is a radius of the circle, we have that angle OGC = 90º and angle ODF = 90º. Thus, triangle ODF is similar to triangle OBC by AA similarity criteria (corresponding angles are equal). Therefore, by the Basic Proportionality Theorem, we conclude that DF || BC.

Step 2

Determine: (a) The ratio of BC : DF.

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Answer

Using the triangles ODF and OBC, since DF || BC, we have:

BCDF=OBOD=53\frac{BC}{DF} = \frac{OB}{OD} = \frac{5}{3} Thus, the ratio of BC : DF is 5 : 3.

Step 3

(b) The length of EG.

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Answer

Given that OD = OE and OB = OG, we can find EG:

EG=OEEGEG = OE - EG Substituting the values:

EG=63.6=2.4EG = 6 - 3.6 = 2.4 Therefore, the length of EG is 2.4 units.

Step 4

(c) The numerical value of Area Δ OBG / Area Δ ODE.

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Answer

To find the areas, we use:

Area of triangle = \frac{1}{2} \times base \times height.

( Area (\Delta OBG) = \frac{1}{2} (6)(3.6) = 10.8 ) ( Area (\Delta ODE) = \frac{1}{2} (8)(2) = 8 )

Thus,

Area(ΔOBG)Area(ΔODE)=10.88=1.35\frac{Area(\Delta OBG)}{Area(\Delta ODE)} = \frac{10.8}{8} = 1.35 The numerical value of Area Δ OBG / Area Δ ODE is approximately 1.35.

Step 5

Show, with reasons, that Δ DOE || Δ BOG.

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Answer

In triangles DOE and BOG, since DF || BC, angles DOF and BGO are equal by the Alternate Interior Angles Theorem. Additionally, angles ODE and OBG are also equal because they are both right angles. Therefore, by AA similarity, we have that Δ DOE || Δ BOG.

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