Преобразовать в сумму:
1)cos 7pi/12*cos pi/12
2)2sin(x-a)*cos(x-a)
1)cos 7pi/12*cos pi/12=cos (7p/12+p/12)+cos (7/12p-1/12p)/2=(cos2/3p )/2+ (cos 1/2p)/2
2)2sin(x-a)*cos(x-a)=(sin(x-a+x-a)+sin(x-a-x+a) )/2=1/2*sin(2x-2a)+0=1/2 sin2x*cos2a+1/2sin2a*cos2x
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Answers & Comments
1)cos 7pi/12*cos pi/12=cos (7p/12+p/12)+cos (7/12p-1/12p)/2=(cos2/3p )/2+ (cos 1/2p)/2
2)2sin(x-a)*cos(x-a)=(sin(x-a+x-a)+sin(x-a-x+a) )/2=1/2*sin(2x-2a)+0=1/2 sin2x*cos2a+1/2sin2a*cos2x