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Prove that : cosA+cos(120^(@)-A)+cos(120...

Prove that : `cosA+cos(120^(@)-A)+cos(120^(@)+A)=0`

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SUBHASH PUBLICATION-TRIGONOMETRY-Prove the following
  1. (cos 75^(@)+cos15^(@))/(sin75^(@)-sin 15^(@))=sqrt(3)

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  2. (sin6A+sin2A+2sin4A)/(sin7A+sin3A+2sin5A)=(sin4A)/(sin5A)

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  3. Prove that : cosA+cos(120^(@)-A)+cos(120^(@)+A)=0

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  4. cos^(2)theta+cos^(2)(60^(@)+theta)+cos^(2)(60^(@)-theta)=3/2

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  5. Show that:4sinA.sin(60^(@)+A)sin(60^(@)-A)=sin3A

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  6. If A+B+C=pi, Prove that tanA+tanB+tanC=tanA.tanB.tanC

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  7. cos20^(@).cos40^(@).cos60^(@).cos80^(@)=1/16

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  8. If A+B+C=pi prove that "tan"A/2"tan"B/2+"tan"B/2"tan"C/2+"tan"C/2"tan"...

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  9. If A+B+C=pi, prove that sin 2A+sin 2B+sin 2C=4 sinA sin B sinC.

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  10. Prove that: sinA+sinB+sinC=4cos(A/2)cos(B/2)cos(C/2) if A + B +C =180 ...

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  11. cos^(2)A+cos^(2)B-cos^(2)C=1-2sinA sinB cosC

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  12. In DeltaABC, prove that (sin(B-C))/(sin(B+C))=(b^(2)-c^(2))/(a^(2))

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  13. (a^(2)-b^(2))/(c^(2)-a^(2))=c/b . (sin(A-B))/(sin(C-A))

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  14. (cos2A)/(a^(2))-(cos2B)/(b^(2))=1/(a^(2))-1/(b^(2))

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  15. Sigmaa sin (B-C)=0

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  16. If a sin a=b sin B then prove that Delta ABC is isosceles.

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  17. If a cosA=b cos B then prove that Delta ABC is eitherisosceles or righ...

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  18. In DeltaABC if (cosA)/a=(cosB)/b=(cosC)/c Prove that DeltaAB C is equi...

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  19. Prove that a^(2)+b^(2)+c^(2)=2(ab cos C +bc cosA +ca cos B)

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  20. (cosA)/a+(cosB)/b+(cosC)/c=(a^(2)+b^(2)+c^(2))/(2abc)

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