6.5 	c) limit (cos x) / x where x to pi
	d) limit x*sin(1/x) where x to 0

6.6	c) limit (x^2+x)/(x^3+1) where x to -1
	d) limit (x^2-2x-3)/(3-x) where x to 3
	j) limit (x+1)/(sqrt(x^2-4)) where x to -1

6.7	a) limit (sqrt(x)-1)/(x-1) where x to 1
	g) 	limit (x-sqrt(x^2-x)) where x to infty
		plot (x-sqrt(x^2-x)) where x from 0 to 100


6.8	b) 	limit x^2/(x+1) where x to infty
		plot x^2/(x+1) where x from 0 to 100
	d)	limit sqrt(x^2+1)/(x) where x to -infty
		plot sqrt(x^2+1)/(x) where x from -1 to -100
	h)	limit 1/(x^2-7x+1) where x to infty
		plot 1/(x^2-7x+1) where x from 0 to 100

6.15	e)	limit (1-cos x)/x^2 where x to 0
	i)	limit (sin(3x))/x where x to infty
		plot (sin(3x))/x where x from 1 to 100
	n)	limit ((x+1)/(x-2))^(3x-2) where x to -infty
		plot ((x+1)/(x-2))^(3x-2)  plot e^9 where x from -10000 to 0

6.16	b)	limit (x+2)/(1-sqrt(x+3)) where x to -2
	i)	limit (cos x)/(cos x -1) where x to 0

6.20	b)	plot sqrt(x/(x-2))
	d)	Plot[Piecewise[{{x^3, x<2}, {4 x, x>2}}],{x,-1,4}]

6.21	c)	Plot[Piecewise[{{3+(-1)*x^2, x<=1}, {x+1, x>1}}],{x,-1,2}]
	d)	Plot[Piecewise[{{x-2, x<=1}, {cos(pi*x), x>1}}],{x,0,2}]