Question 1011265
by definition, {{{cos(A-B) = cos (A) cos (B) + sin( A) sin( B)}}}

so,  if {{{sin(A) sin (B) = cos (A) cos (B)}}}, then

{{{cos(A-B) = cos( A) cos (B) + cos (A) cos (B)}}}

{{{cos(A-B) =2 cos( A )cos (B )}}}