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.


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