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## Homework Statement

Its actually not a homework , i am just curious about this

I have disc with a hole in middle , R1 is inner radius , R2 is outer radius , Mass M is the disc's mass . Let density of disc uniform .

I did it this way . -

λ.dA=dm

λ.pie.r.dr=dm as Area=pie.r^2

Let substute in the equation I = ∫( R^2).dm

therefore I = ∫( p.pie.r^3 ).dr

remove constants outside the integral therefore I =λ.pie∫r^3.dr

integrate (0 to R )to get I = λ.pie.r^4/4

using Mass = λ*pie*r^2

therefore i get I = (MR^2)/4 for thin Disc

As i have a hole therefore its I = M(R2^2-R1^2)/4

But sadly this is incorrent :/ . It seems that I = M(R2^2-R1^2)/2 is the correct solution

Please Help !!!!!!!!!!!! :O why my way is wrong :(