curve(x^2, 0, 10, col='blue', xlab='x', ylab='f(x)')
grid() 
curve(25*sqrt(x), 0, 10, col='red', add=TRUE)
curve(3*exp(0.333*x), 0, 10, col='green', add=TRUE)
curve(20*x^1, 0, 10, col='brown', add=TRUE)

text(4, 89, 'A', col='brown', cex=1.7)
text(6, 66, 'B', col='red', cex=1.7)
text(5, 32, 'C', col='blue', cex=1.7)
text(8.3, 40, 'D', col='green', cex=1.7)