This very simple demo allows students to visualize points on the complex plane in polar form (re^ix)
point z is defined as r*exp(a/b * pi i) where a,,b, and r are controlled by sliders
point z_2 is on the same circle (has radius r) but can be dragged around the circle to see what the angle in radians is
I knowledge of Euler's formula helps students connect trigonometry, complex numbers, and calculus (including Maclaurin series) and I believe it should be introduced as early as possible into a high school pre-calculus curriculum