Ok, i think that i asked the question in a wrong way.. I did mean the physical interpretation of "taking square" as Hootenanny said above.
Could you help me about this question, at least a personal idea or expression?
Taking square?
Why do we need to take square? What does it mean? For instance, calculating energy, why do we need to take square of the velocity or taking square of time in some other formulas?
In general, what is the mathematical meaning of taking square?
I took a look at John Lamarsh's book; Int. to Nuclear Engineering but there is not a exact clue to solve tihs problem.. Also i could got nothing on the net. Its very simple to make a prediction about this but what is the exact proof behind this situation..
The compositions of nuclear reactors are often stated in volume fractions. i.e the fractions of the volume of some region that are composed of particular materials. Show that the macroscopic cross section for the equivalent homogeneous mixture of materials is given by
∑a = f1 ∑a1 + f2∑a2 +...