#####################
# Rotating triangle #
#####################
# for more fun, check out https://www.youtube.com/watch?v=sW9npZVpiMI


x = c(0, 2, 3)
y = c(0, 7, 5)
oldtriangle = rbind(x,y)

theta = pi/2
rotate.matrix = matrix(c(cos(theta),-sin(theta),sin(theta),cos(theta)),nrow=2,byrow=T)
newtriangle = rotate.matrix%*%oldtriangle

plot(x, y, type = "p", pch = 16, col = "blue", xlim = c(-7, 7), ylim = c(-7, 7))
polygon(x, y, col = "red", border = "blue")
polygon(newtriangle[1,], newtriangle[2,], col = "black", border = "green")