allerycos(A + B) equals:
AcosA cosB + sinA sinB
BcosA cosB - sinA sinB
CsinA cosB + cosA sinB
DcosA + cosB
Answer & Solution
Correct answer: B. cosA cosB - sinA sinB
cos(A + B) = cosA cosB - sinA sinB.
(Note: cos(A - B) = cosA cosB + sinA sinB — sign change.)
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