In an extracurricular practice activity, students need to measure the distance between two pavilions A and B on both sides of an artificial lake in a park. Now, AC = 30m, BC = 70m, ∠ cab = 120 ° are measured. Please calculate the distance between two pavilions A and B

As shown in the figure, make CD ⊥ AB at the point D. in RT △ CDA, AC = 30m, ∠ CAD = 180 °- ∠ cab = 180 ° - 120 ° = 60 °. In RT △ CDB, ∵ BC = 70, BD2 = bc2-cd2, ∵ BD = 702 − (153) 2 = 65m. ∵ AB = bd-ad = 65-15 = 50m

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