JEE Main 2013 (Online) 9th AprilQuestion 1
The vector $\left(\hat i\times\vec a\cdot\vec b\right)\hat i+\left(\hat j\times\vec a\cdot\vec b\right)\hat j+\left(\hat k\times\vec a\cdot\vec b\right)\hat k$ is equal to :
Vector Algebra
Solution
$(\hat i\times\vec a)\cdot\vec b=\hat i\cdot(\vec a\times\vec b)$, so the sum is $\sum(\hat i\cdot(\vec a\times\vec b))\hat i=\vec a\times\vec b$.