This song is available on Triangle Head by The Trigs.

This song explores the congruence and the maintenance of proportions. It covers how to set up and solve proportions (cross-multiply and divide) through two examples: enlarging a photograph and enlarging a triangle.

I've got a photograph that I want to enlarge
Right now the width is 6 inches i want it to be 9
So if the length is 4, then what will it become?

Let's make two ratios and solve our proportion
I'll put new over old so there's the 9 over the six
and on the other side I'll put the 4 under the x
When I cross-multiply I will have 9 times 4
And then I will divide by 6 and finally I'll solve

Chorus:
A proportion is two ratios that are congruent to each other
To solve you just cross-multiply and divide
The secret how to do it right make sure corresponding part align
And then it's easy to find the missin' parts

So what if I have two similar triangles?
I know the bases are 12 feet and 4
The height of the small triangle is 6
So let's find what the height of the other one is"

So for our ratios lets put the small over the large
On the left we've got 4 feet and it is over the 12
On the right's 6 over x so let's cross-multiply
Now we've got 12 times 6 and let's divide by 4

Bridge:
So my new photo was 9 inches by 6
and my new triangle was 18 feet high
Proportions are easy once you know how to solve
Just remember that you've got to cross-multiply and divide

See more of our Songs that Teach about Advanced Math

Many thanks to The Trigs for permission to display these lyric excerpts.
© The Trigs. All rights reserved. Used with permission.

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