Baka to Tesuto to Syokanju:Volume10 The Fifth Question

The Fifth Question

Please answer the following question:

Please calculate the area of the shaded region. Use π as the circular constant.

Himeji Mizuki answer:

Assuming that the radius of the small circle is r, and the circumference as ℓ.

ℓ = 2 π r

The question asks for the area between radius 1 and 3, so we’ll call it ‘S’.

S= Failed to parse (syntax error): {\displaystyle \int_1^3 2 π r \;dr }