Answer
$(i+j ) \times (i-j)=-2k$
Work Step by Step
Cross product of a vector with itself is zero.
We are given $(i+j ) \times (i-j)$
$(i+j ) \times (i-j)=i \times (i-j)+j \times (i-j)$
$=i \times i-i \times j+j\times i-j \times j$
$=0-k+(-k)+0$
$=-2k$
Hence, $(i+j ) \times (i-j)=-2k$
