Question

cos (A - B) + cos (2A + B) =​

Answer 1

Answer:

cos(A-B)+ cos(2A+B)

= cosA cosB - sinA sinB + cos2A cosB - sin2A sinB

$\cos(a) \cos(b) - \sin(a) \sin(b) + { \cos }^{2} a \: cosb \: - { \sin }^{2} a \: cosb - 2 \sin(a) cosa \: sinb \\ \\ = cosa \: cosb(1 + cosa) - sina \: sinb(1 + 2cosa) + cosb - 2 { \sin }^{2} a \: cosb$