Question

find (A vector + B vector).(A vector- B vector )​

Answer 1

Solution:

We know that if a be any vector, then

a . a = a² = |a|²

Now, (A + B) . (A - B)

= A . (A - B) + B . (A - B)

= A . A - A . B + B . A - B . B

= A² - B² [ since A . B = B . A ]

= |A|² - |B|²