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A similarity transformation is a dilation or a sequence of dilations and rigid motions.
What is the relationship between side lengths in similar figures? Is it the same as the relationship between the heights?
Yes
Yes, see solution.
We are asked to use a ruler to draw two different isosceles triangles that are similar to the given one. Then, we want to find if the ratios of the corresponding heights are equivalent to the ratios of the corresponding side lengths. Let's do these things, one at a time.
Let's take a look at the given triangle.
For the first triangle, let's choose k= 2.
(x,y) | (2x,2y) | Simplify |
---|---|---|
(0,0) | ( 2*0, 2*0) | (0,0) |
(3,4) | ( 2*3, 2*4) | (6,8) |
(6,0) | ( 2*6, 2*0) | (12,0) |
We can plot the new vertices on the coordinate plane and connect them using a ruler to draw the first triangle. We will also measure its height and sides.
For the second triangle, let's choose k= 0.5.
(x,y) | (0.5x,0.5y) | Simplify |
---|---|---|
(0,0) | ( 0.5*0, 0.5*0) | (0,0) |
(3,4) | ( 0.5*3, 0.5*4) | (1.5,2) |
(6,0) | ( 0.5*6, 0.5*0) | (3,0) |
Again, we can plot the new vertices on the coordinate plane, connect them, and measure its height and sides.
Now we will consider the ratios of the original triangle and the new triangles. Let's find the ratios of the corresponding side lengths of the original triangle and the first similar triangle that we drew. The lengths of the sides in the original triangle are 5 and 6. The corresponding side lengths in the first similar triangle are 10 and 12. 5/10 = 6/12 = 1/2 The height of the original triangle is 4 and the height of the first similar triangle is 8. 4/8 = 1/2 We can see that the ratios are equivalent. Now, let's check the ratios for the second similar triangle that we drew. The corresponding side lengths to the sides of measures 5 and 6 are 2.5 and 3. 5/2.5 = 6/3 = 2 The height of the original triangle is 4 and the height of the second similar triangle is 2. 4/2 = 2 We can see that the ratios of the corresponding heights are equivalent to the ratios of the corresponding side lengths.
(x,y) → (kx,ky) This means that also the endpoints of the height follow this dilation and, because of that, the heights are multiplied by the same number as the sides. Therefore, it is true that for all similar triangles the ratios of the corresponding heights are equivalent to the ratios of the corresponding side lengths.