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    				| 1. | If `P`is a pointand `A B C D`is aquadrilateral and ` vec A P+ vec P B+ vec P D= vec P C`, show that `A B C D`is aparallelogram. | 
| Answer» We can draw a diagram with the given details. Please refer to video to see the diagram. It is given that, `vec(AP) +vec(PB) +vec(PD) = vec(PC) ` `=>vec(AP) +vec(PB) = vec(PC) - vec(PD)->(1)` Now, in `Delta PDC`, `vec(PD)+vec(DC) = vec(PC)` `=>vec(DC) = vec(PC) - vec(PD)->(2)` Now, in `Delta PAB`, `vec(AP)+vec(PB) = vec(AB)->(3)` From (1),(2) and (3), `vec(AB) = vec(DC)` It implies that `ABCD` is a parallelogram. | |