-->

Vector Algebra

Question
CBSEENMA12033958

If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top space and space straight d with rightwards arrow on top are distinct non-zero vectors represented by directed lines from the origin to the points A, B, C and D respectively and if straight b with rightwards arrow on top minus straight a with rightwards arrow on top space equals space straight c with rightwards arrow on top space minus space straight d with rightwards arrow on top, then prove that ABCD is a parallelogram.

Solution

Here  straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top comma space straight d with rightwards arrow on top are the position vectors of A, B, C, D respectively with reference to O as origin
Now,             straight b with rightwards arrow on top minus straight a with rightwards arrow on top space equals space straight c with rightwards arrow on top minus straight d with rightwards arrow on top
rightwards double arrow space space space space space space OB with rightwards arrow on top space minus space OA with rightwards arrow on top space equals space OC with rightwards arrow on top space minus space OD with rightwards arrow on top
rightwards double arrow space space space space space space space space space space space AB with rightwards arrow on top space equals space DC with rightwards arrow on top
therefore space space space space space space AB space equals space DC space and space AB vertical line vertical line DC
therefore space space space space space ABCD space is space straight a space parallelogram.