Isosceles If You Please
copyright 2013 by Tim Griffin

You tell me triangles have three sides and angles
I tell you triangles are not all the same
It’s true each triangle has three sides and angles
But different triangles have different names

The first one I speak will have three sides not equal
It’s only a scalene, I’m sorry to say
When three sides are different, I’m really indifferent
You give me a scalene, I’ll throw it away

(chorus) But my favorite triangle has two equal angles
And two equal sides, which is clearly implied
There’s only one triangle certain to please
With two equal sides, it’s an isosceles!

There’s another triangle that I find offensive
With three equal angles and three equal sides
I despise equilaterals, wish they would all be gone
The boringest polygon I’ve ever tried

Stow all your chatter, I’ll have no equilateral
The three equal sides only bore me to tears
I’m telling you kid, a Greek guy named Euclid
Described all those triangles two thousand years… ago

(repeat chorus)

There are one hundred eighty degrees in a triangle
Add up the angles and you will agree
It’s a right triangle if there’s an angle
That measures exactly ninety degrees

If all of the angles are less than right angles
You don’t say it’s wrong, you just call it acute
More is obtuse but I say what’s the use,
If it doesn’t have two equal sides to salute

(repeat chorus)

(coda) I’m finally satisfied, grateful and gratified
Satisfied since I saw isosceles!


There are so many specific terms for the different types of triangles, I thought we should have a song just for their definitions. Of course, I don’t really have a strong preference for any one triangle; I just figured it would make the song more interesting if I wrote it as an advocacy song. That's called a literary conceit, and just one example of the fine lyrical edification you get here at GriffinEd.

Here are some standards from the Common Core and the state of California addressed by this song:

Grade 3:

  • CCSS.MATH.CONTENT.3.G.A.1 Understand that shapes in different categories (e.g., rhombuses, rectangles, and others) may share attributes (e.g., having four sides), and that the shared attributes can define a larger category (e.g., quadrilaterals).
  • CA Math, grade 3.2.1 Identify, describe, and classify polygons (including pentagons, hexagons, and octagons).
  • CA Math, grade 3.2.2 Identify attributes of triangles (e.g., two equal sides for the isosceles triangle, three equal sides for the equilateral triangle, right angle for the right triangle).

Grade 4:

  • CCSS.MATH.CONTENT.4.G.A.1 Draw points, lines, line segments, rays, angles (right, acute, obtuse), and perpendicular and parallel lines. Identify these in two-dimensional figures.
  • CCSS.MATH.CONTENT.4.G.A.2 Classify two-dimensional figures based on the presence or absence of parallel or perpendicular lines, or the presence or absence of angles of a specified size. Recognize right triangles as a category, and identify right triangles.
  • CA Math, grade 4.3.7 Know the definitions of different triangles (e.g., equilateral, isosceles, scalene) and identify their attributes.

Grade 5:

  • CCSS.MATH.CONTENT.5.G.B.3Understand that attributes belonging to a category of two-dimensional figures also belong to all subcategories of that category. For example, all rectangles have four right angles and squares are rectangles, so all squares have four right angles.
  • CCSS.MATH.CONTENT.5.G.B.4 Classify two-dimensional figures in a hierarchy based on properties.
  • CA Math, grade 5.2.1 Measure, identify, and draw angles, perpendicular and parallel lines, rectangles, and triangles by using appropriate tools (e.g., straightedge, ruler, compass, protractor, drawing software).
  • CA Math, grade 5.2.2 Know that the sum of the angles of any triangle is 180°

C, F, Am, G, D. I often use a capo to transpose it up a half step.