Express each of the following as sum or difference form. 2sinA.sinB
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NANBA..
L.H.S=cosx+cos(120-x) +(120+x)
=cosx+2cos120.cos5x {चुकि =cos(A+B)=cos(A-B) =-2sinA.sinB}
=cosx+(-2cos(180-60)cosx
=cos-2.1/2.cosx
=cosx-cosx
=0 R.H.S proved
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