secθ= 1/cosθ 1)sinA+sinB=2cosA+B/2*sinA-B/2 2)sinA-sinB=2sinA+B/2*cosA-B/2 3)cosA+cosB=2CosA+B/2*cosA-B/2 4)cosA-cosB=-2SinA+B/2*sinA-B/2
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