Show that for a , b , c , d ∈ R {\displaystyle {}a,b,c,d\in \mathbb {R} } satisfying a 2 + b 2 + c 2 + d 2 = 1 {\displaystyle {}a^{2}+b^{2}+c^{2}+d^{2}=1} , the matrix
defines an isometry on R 3 {\displaystyle {}\mathbb {R} ^{3}} .