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Question
If C is the midpoint of AB and P is any point outside AB, then ______
Options
`overline"PA" + overline"PB" + overline"PC" = overline0`
`overline"PA" + overline"PB" + 2overline"PC" = overline0`
`overline"PA" + overline"PB" = overline"PC"`
`overline"PA" + overline"PB" = 2overline"PC"`
Solution
If C is the midpoint of AB and P is any point outside AB, then `underline(overline"PA" + overline"PB" = 2overline"PC")`.
Explanation:
By using triangle law of addition of vectors in triangles PAC and PBC, we have
`overline"PA" + overline"AC" = overline"PC"` and `overline"PB" + overline"BC" = overline"PC"`
⇒ `overline"PA" + overline"AC" + overline"PB" + overline"BC" = overline"PC" + overline"PC"`
⇒ `overline"PA" + overline"PB" + (overline"AC" + overline"BC") = 2overline"PC"`
⇒ `overline"PA" + overline"PB" + (overline"AC" - overline"AC") = 2overline"PC"`
⇒ `overline"PA" + overline"PB" = 2overline"PC"`