#====================
# Figure 9.4.R.
# Right triangle inscribed in a circle--
# upper left quadrant.
#====================
theta=(0:200)*2*pi/200
y=sin(theta)
x=cos(theta)
par(pin=c(4,4))
plot(x,y,type="l",axes=FALSE,ann=FALSE)
abline(h=0)
abline(v=0)
th=pi-4*pi/18
x0=c(0,cos(th),cos(th))
y0=c(0,sin(th),0)
x1=c(cos(th),cos(th),0)
y1=c(sin(th),0,0)
segments(x0,y0,x1,y1,lwd=2)

th=4*pi/18
# text(-.6*cos(th),-.1,expression(italic(-x)),cex=1.5)
# text(-(cos(th)+.1),.4*sin(th),expression(italic(y)),cex=1.5)
text(-cos(th)/2,.4,expression(italic(r)),cex=1.5)
text(.1*cos(th),.1,expression(theta),cex=1.5)

text(-(cos(th)+.12),sin(th)+.12,
  expression((list(italic(x),italic(y)))),cex=1.5)

text(.24*cos(th),-.1,expression((list(0,0))),cex=1.5)