Created a program in Mathematica that animates the unit cicle to help visualize the values of trigonometric functions (sin(x), cos(x), tan(x)).
Manipulate[
Graphics[{Line[{{0, 0}, {Cos[x], Sin[x]}}], Circle[],
Line[{{0, 0}, {Cos[x], 0}}], Line[{{1, 0}, {1, Tan[x]}}],
Line[{{0, 0}, {1, Tan[x]}}],
Rotate[Rectangle[{0, 0}, {Sec[x], Sec[x]}],
Degree (57.2*x), {0, 0}], Line[{{Cos[x], 0}, {Cos[x], Sin[x]}}]},
PlotRange -> {{-1.5, 1.5}, {-1.5, 1.5}}], {x, 0, 2*\[Pi]} ]