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## Homework Statement

D1=6cm D2=2cm ( i have to prove that 2nd moment of area (J) of a circulal plate abouts its polax axis(zz) is equal to piD^4/32 )

## Homework Equations

## The Attempt at a Solution

J=pi6^4/32 - pi2^4/32 = 125.66

J=r1^2x2pirdr

J=Integral 2pir^3d2 = 2pi integral(high 3 , low 1) r^3dr=2pi (r^4/4)(high3 ,low1)

=2pi ((3^4/4)-(1^4/4) = 2pi (20.25 - 0.25) = 2pi x20 = 125.66 (answer is correct ) but i need to show how piD^4/32 is derrived using integration