Question

If a and b are two vectors, then the value of $(a\times b)\times (a-b)$ is

• A. $2(b\times a)$
• B. $-2(b\times a)$
• C. $b\times a$
• D. $a\times b$

Answer 1

Answer: (A)

$(a+b)(a-b)=a\times a-a\times b+b\times a-b\times b=0$ $a\times b=-b\times a$ and $a\times a=0$ $(a+b)\times (a-b)=2(b\times a)$