The point (-3,5) is on the terminal side of an angle. What is the sine of that angle?
The formulaic approach is to say that sine (A) = y/r, where r is the radial distance from the point to the origin. But that formula is just for memorizing, so I came up with an alternate explanation about "shrinking" the entire triangle down until it would fit into the unit circle. To do so you'd have to divide all 3 sides by r (in this case, root 34), and the new y-value would be the sine: 5/(root 34), or (5 root 34)/34.
Just seeing the diagram made it very clear to them. And it's the first time I've ever thought to teach it that way, even though I've taught the course, sometimes more than once a year, for 8 different years.