1. The problem statement, all variables and given/known data Determine the moment of inertia of the shaded area about the x axis. 2. Relevant equations Ix=y^2dA 3. The attempt at a solution Okey so I now get how to do this the standard method. But I want to know if the method I tried is correct aswell or where my mistake lies. My attempt: I look at the portion above x-axis and then multiple it with 2. So I tried to use the method that I have been taught, a small element that touches the graph like in the picture. dA= (Rcos (a)- X)dady since x^2+y^2=R^2, x= sqrt (R^2-y^2) so I(x)= y^2(Rcos(a)-sqrt (R^2 - y^2))dady First I integrate this to da with the limits 0 to 1/2a (since the angle goes from 0 to 1/2a) and then that answer I integrate to dy with limits 0 to Rsin(a/2) (since y goes from 0 to Rsin(a/2) So basically after the first integration I get: y^2Rsin(a/2)-(a/2)(y^2)sqrt(R^2-y^2)dy and then when I integrate this I get this very long and quite complicated equation but is it correct? I know now the simpler way, but I find it important that I understand it.