Question

Given Triangle ABC with FC=5, you want to find BF. First, find the value that y must have for the Triangle Proportionality Theorem to apply. Then describe more than one way to find BF, and find BF. The y value for the Triangle Proportionality Theorem to apply is ______. To find BF, you can use the ______ Formula with the coordinates of B and F l, or you use the Trianglr Proportionality Theorem. BF=

Answer 1

Part A

y = 8

Part B

We can find BF by either;

a) Through Pythagoras theorem to find the length of a side in a right triangle

b) The known rate of change of the length of the line FC with height

Explanation:

Part A

The given parameters are;

FC = 5

We are to find BF

By the triangle proportionality theorem, we have;

FC:BF = EC:AE

From the given draining we have;

C(10, 2), F(7, 6), B(5.5, y), E(4, 2), A(1, 2)

Points A, E and C are have the same y-coordinate values, therefore, we have;

EC = 10 - 4 = 6

AE = 4 - 1 = 3

Therefore, we have;

5/BF = 6/3 = 2

BF = 5/2 = 2.5

Using the formula for finding the distance between two points, we have;

BF = √((5.5 - 7)² + (y - 6)²)

BF² = 2.5² = (5.5 - 7)² + (y - 6)²

6.25 = 2.25 + (y - 6)²

6.25 - 2.25 = 4 = (y - 6)²

√4 = √(y - 6)² = (y - 6)

±2 = y - 6

y = 6 + 2 = 8, or y = 6 - 2 = 4

Given that from the diagram, y > 6, we have y = 8

Part B

a) To find BF we can use the Pythagoras's theorem given that we know the coordinates of B and F as follows;

BF = √((5.5 - 7)² + (8 - 6)²) = 2.5

b) Given that BF is on the same straight line as FC, BF can be found through the rate of change of the y-values with the length of the line

We can also find BF by using proportion of increase in 'Δy' to the length of the line BFC as follows;

From point C to point F, Δy = 6 - 2 = 4 and the length of the line FC = 5

Therefore, from point B to point F, Δy = 8 - 6 = 2, ∴ BF = 2 × 5/4 = 2.5