鍧氭灉r2鏄畨鍗撳嚑

△r=r2-r1

(｀▽′)

r2/√4a2-r2

√1-r2/1+r2rdr

φ2-φ1+2π(r1-r2)/λ=2kπ

r2=acos2θ

ˋ▽ˊ

?﹏?

≡(▔﹏▔)≡