alleryStart learning →Factorising cosC − cosD gives
A2 sin((C+D)/2) sin((C−D)/2)
B−2 sin((C+D)/2) sin((C−D)/2)
C2 cos((C+D)/2) cos((C−D)/2)
D−2 cos((C+D)/2) sin((C−D)/2)
Answer & Solution
Correct answer: B. −2 sin((C+D)/2) sin((C−D)/2)
cosC − cosD = −2 sinA sinB with A = (C+D)/2 and B = (C−D)/2, so the leading sign is negative.
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