According to s, the flash is emitted at A, reflected at b. and detected at c This interva△tis 1s2l2/n2 +(l 2 △ (2020) Substituting for Lo from Eg(20-1)and solving Eq(20-2)for At gives △ △t (/)2 (203)According to S, the flash is emitted at A, reflected at B, and detected at C. This interval is (20-20) Substituting for from Eq(20-1) and solving Eq(20-2) for gives (20-3) c t L u c L t 2 2 0 ) 2 2 ( 2 +   = = 2 0 1 ( ) c u t t −   = t t L0