De dang tinh dk $\lambda =2,5cm$
Nhan thay tren doan $AB$ se co 12 diem dung yen nhu vay ve moi phia cua duong trung truc se co 6
duong cong ma cac diem tren do khong dao dong.
De $M$ thuoc duong tron ma $MA $ lon nhat thi $M$ phai thuoc duong cong xa $A$ nhat (duong thu 6 ve
phia B) khi do ta co:
$d_{1}-d_{2}=5,5\lambda<=>AM-BM=5,5\lambda $
$<=>AM-\sqrt{AB^2-AM^2}=5,5\lambda$
$<=>AM-\sqrt{16^2-AM^2}=13,75$
$<=>AM\approx 15,86cm$