# Friday Five for September 16

The Friday Five is feeling nostalgic this week, and so the Five is digging deep into the activity archives. (Plus, the Friday Five’s colleagues have been more consumed with building awesome new stuff that’s not quite ready for prime time than with polishing up new activities for the search pool (about which, stay tuned!))

Up this week: Calculus, equation solving, slope and trig. Enjoy!

## Differentiability

When is a corner not a corner? Dave Sabol sets up a really wonderful look at corners, and their not-so-intuitive classification. Even if you’re not teaching calculus, there’s something really fun to debate with students here. (And there is also the closely related zoomable heart built by Desmos engineer Denis Lantsman, and intended for elementary use.)

## Solving Equations with Number Properties

This activity is from Desmos’s own Shelley Carranza (from before she was Desmos’s own!) If you wish for your students to develop meaning for their solutions to equations in one variable, then Shelley helps you get the conversation started here!

## Match My Trig Function (Degrees)

Jon Orr has graced this blog before, and does so again today with this activity. Build up students’ skills to prepare them to settle an argument at the end!

## Connect the Dots (Trig Style!)

You want more trig?!? Who doesn’t? Natalie Holm has what you need. Where Match My Trig Function challenges students to trace a dotted line, Connect the Dots challenges them to imagine what function could go through all of these points. Is each solution unique? Is an important question here.

## Point, Point, Slope

Finally, Christopher Kunkel gives us this Open Middle-style activity. You’re given a set of digits, places to plug them in, and a challenge—place two points so that the slope is minimal, or maximal, and by the way is it possible to make it horizontal?

Whatever math interests you—whether it’s calculus, trigonometry, algebra, or anything else—the Friday Five wishes you a restful, homework-free weekend. Cheers!