PLZ HELP RN. why do we learned about triangles before parallelograms?

What is the length of the unknown leg in the right triangle ?

What could explain what happened when the time was equal to 120 minutes

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