What I Have Learned About Grade 9 Similarity

This blog post represents what I have learned in this similarity unit.

What is an Enlargement and a Reduction?

An enlargement is to make an original object bigger and a reduction is to make an original object smaller.
We use multiplication to create an enlargement or reduction for an object.
Examples of enlargements: Any numbers over 1, impropre fractions, percentages over 100%
Examples of reductions: Any numbers under 1, propre fractions, percentages under 100%
If the scale is 1 or 100%, that means that is not an enlargement nor a reduction and actually stays the same.

It is a ration that demonstrates two corresponding lengths in two figures.
For the scale factor, the original length goes on the bottom and the length in the original goes on the top.

Here is an example of a question including a scale factor.
What is the actual length of an object if the scale is 1:10 and the length of the object in the diagram in 4?

$\frac{1}{10}$ $\frac{4}{x}$

$\frac{1x}{1}$ $\frac{40}{1}$ x=40

Similar triangles are triangles with equal corresponding angles and proportionate sides.
To figure out if two triangles are similar, you have to create ratios that correspond to the sides. If they equal the same number, they are similar but if they do not, then they are not similar.
To figure out a missing side length from a similar triangle, you have to use the butterfly technique (multiplying the information in a cross like formation).

To figure out how to measure and object is taller than you are, you can use this technique by using a mirror.
You place a mirror on the ground and measure how tall you are from your eyes, the distance between where you are standing and the mirror and the distance between the mirror and the object.