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VERSIN(A+B)*VERSIN(A-B)
[1-cos(A+B)][1-cos(A-B)]
1-cos(A-B)-cos(A+B)+cos(A+B)cos(A-B)
1-(cosAcosB+sinAsinB)-(cosAcosB-sinAsinB)+(cosAcosB-sinAsinB)(cosAcosB+sinAsinB)
1-cosAcosB-sinAsinB-cosAcosB+sinAsinB+(cosAcosB-sinAsinB)(cosAcosB+sinAsinB)
1-2cosAcosB+(cos²Acos²B-sin²Asin²B)
1-2cosAcosB+cos²Acos²B-sin²Asin²B
1-2cosAcosB+cos²Acos²B-(1-cos²A)(1-cos²B)
1-2cosAcosB+cos²Acos²B-(1-cos²B-cos²A+cos²Acos²B)
1-2cosAcosB+cos²Acos²B-1+cos²B+cos²A-cos²Acos²B
-2cosAcosB+cos²B+cos²A
cos²A-2cosAcosB+cos²B
(cosA-cosB)²
Edwin