Chapter 12 - Vectors and the Geometry of Space - 12.4 The Cross Product - 12.4 Exercises - Page 861: 11

$(j-k ) \times (k-i)=i+j+k$

Cross product of a vector with itself is zero. As we are given that $(j-k ) \times (k-i)$ $(j-k ) \times (k-i)=j \times (k-i)-k \times (k-i)$ $=j \times k-j \times i-k\times k+k \times i$ $=i-(-k)-0+j$ $=i+j+k$ Hence,$(j-k ) \times (k-i)=i+j+k$