Compute &#x222C;<!-- ∬ --> D </msub> x 2 </msup> <msqrt>

skottyrottenmf

skottyrottenmf

Answered question

2022-05-19

Compute
D x 2 1 + x 2 + y 2 d x d y
where D = { ( x , y ) | x 2 + y 2 1 , x 0 }

Answer & Explanation

exhumatql

exhumatql

Beginner2022-05-20Added 12 answers

D x 2 1 + x 2 + y 2 d x d y = 0 1 π 2 π 2 r 3 cos 2 ( θ ) 1 + r 2 d θ d r = 0 1 r 3 1 + r 2 d r π 2 π 2 cos ( 2 θ ) + 1 2 d θ
Now, we have
π 2 π 2 cos ( 2 θ ) + 1 2 d θ = π 2
and
0 1 r 3 1 + r 2 d r = 1 2 0 1 u 1 + u d u ( u = r 2 ) = 1 2 1 2 s 1 s d s ( s = 1 + u ) = 1 2 1 2 s 1 2 s 1 2 d s = 2 3 ( 2 2 )
giving a final answer of π ( 2 2 ) 3 . There might be some mistake which I'm not aware of which causes the answer not to be the one you claimed.

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