difference between xsectional area and surface area

[mytoechondriac]

I'm sorry for this stupid question, but I keep getting the X-sectional area and the surface area confused. I know for a sphere, the surface area is 4(pi)r^2, but how do I calculate the X-sectional rea for the sphere? Is it pi(r^2)?

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[engineeredout]

Well think about what a cross section of a sphere would be; its a circle. So area of a circle is pi*r^2 or pi*(d^2)/4

That applys to the face of the cross section. Since the cross section can technically be taken at any point you're probably not going to have to concern yourself with the area of the sphere behind the face.

 

[ecoli]

just to add to the above... it seems like your stuck on just memorizing the equations. Put the equations in context. Keep in mind that all these geometry equations have calculus proofs. That means that the equation is grounded in some physical aspect of the shape.

If they ask you a question about an equation you haven't memorised, see if you can't figure it out, or approximate an answer, using dimensional analysis. (compare the units of givens against what the question is asking for, for example).