show that costita+cos(120+tita)+cos(240+tita)=0
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Answer:
Step-by-step explanation:
LHS= CosA+Cos(120+A)+Cos(240+A)
=CosA+Cos{180-(60-A)}+Cos{180+(60+A)}
=CosA-Cos(60-A)-Cos(60+A)
=CosA-{cos60cosA+Sin60SinA}-{Cos60CosA-Sin60SinA}
=CosA-(CosA/2)-(√3/2)SinA-(CosA/2)+(√3/2)SinA
=CosA-(2CosA/2)
={2CosA-2 CosA}/2
=0
Therefore LHS=RHS
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