What’s the missing value (using the pythagorean theorem)

What are “like terms”? why can we only add like terms?

Find the volume of the described solid.the solid lies between planes perpendicular to the x-axis at x = 0 and x=7. the cross sectionsperpendicular to the x-axis between these planes are squares whose bases run from the parabolay=-31x to the parabola y = 30/x.a) 441b) 147c) 864d) 882

What can you determine about the solutions of this system