Question

The endpoints of line segment AB are A (9,4) and B (5,-4). Then endpoints of its image after dilation are A' (6,3) and B' (5,-4). Find the scale factor and explain

Answer 1

To find our scale factor, let's determine the length of AB, and compare it to the length of A'B'.

The length of AB is the distance from (9,4) to (5,-4). 
Let's apply the distance formula:
AB = √ ((9-5)² + (4+4)²)
AB = √ (4² + 8²)
AB = √(16 + 64)
AB = √ (80)
AB = 4 √5
The length of AB is 4 √5.
Now for A'B':
A'B' = √ ((6-5)² + (3+4)²)
A'B' = √( 1 + 49)
A'B' = √ 50
A'B' = 5 √2
To find our scale factor k:
A'B' = k AB
5 √2 = 4 √5 * k Divide both sides by 4√5
5 √2 / (4 √5) = k                 To simplify, multiply the left side by (√5 / √5)
(5 *√5 * √2) / (4 *5) = k      the 5's in the numerator and denominator cancel
√5 * √2 / 4 = k                    
√10 / 4 = k

To confirm, make sure AB * k = A'B', using the values that we've calculated.

Answer 2

Answer:To find the image of B, first find the scale factor for the dilation. The scale factor should be greater than 1 because the image of A is farther from the origin than A. Divide the coordinates of the image of A by the coordinates of A: –6/–4 = 3/2 and 9/6 = 3/2, so the scale factor is 3/2. Now, apply the dilation to B by multiplying the coordinates by 3/2 to get ((3/2)(1), (3/2)(4)), or (3/2, 6).

Hope I helped