Homework, 7.8. #3, 47, 51

N[Integrate[1/x^3,{x,1,10}]]
N[Integrate[1/x^3,{x,1,100}]]
N[Integrate[1/x^3,{x,1,1000}]]

Integrate[1/x^3,{x,1,Infinity}]

#47, p. 551

N[Integrate[(Sin[x]/x)^2,{x,1,{2,5,10,100,1000,10000}}]]

Plot[{(Sin[x]/x)^2,1/x^2},{x,1,10}]

#51, p. 552

Integrate[(x+1)/Sqrt[x^4-x],{x,1,Infinity}]