#1. feladat: f(x) = 2cos(2x)−1
x = seq(0,4*pi,pi/16)
y1 = cos(x)
y2 = cos(2*x)
y3 = 2*y2
y4 = y3-1
plot(x,y1,type="l",ylim=c(-3,2),xlim=c(0,16),ylab="y")
lines(x,y2,col="blue",lty=4)
lines(x,y3,col="purple")
lines(x,y4,col="red",pch=5,type="o")
legend(13,2,c("cos(x)","cos(2x)","2cos(2x)","2cos(2x)-1"),
	lty=c(1,4,1,1),pch=c(NA,NA,NA,6),col=c("black","blue","purple","red"))