Question

Cross product of $(a-b)\times (a+b)$ is equal to

• A. $\frac{2}{3}(a\times b)$
• B. $(a\times b)$
• C. $2(a\times b)$
• D. None of these

Answer 1

Answer: (C)

$(a-b)\times (a+b)$
$=a\times a+a\times b-b\times a-b\times b$
$=0+a\times b+a\times b-0(\because a\times a=0$ and $a\times b=-b\times a)$
$=2(a\times b)$ Hence proved.