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Prove that SinA-sin3A+sin5A-sin7A/cosA-cos3A-cos5A+cos7A=cot2A. |
Answer» L.H.S = sinA-sin3A+sin5A-sin7A/cosA-cos3A-cos5A+cos7A = -(sin7A-sinA)+sin5A-sin3A/cos7A+cosA-(cos5A+cos3A) = -2cos4A*sin3A+2cos4A*sinA/2cos4A*cos3A-2cos4A*cosA = 2cos4A(sinA-sin3A)/2cos4A(cos3A-cosA) = sinA-sin3A/cos3A-cosA = -2sinA*cos2A/-2sinA*sin2A = cos2A/sin2A = cot2A = R.H.S | |