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Find the value of `cos(2pi)/7+cos(4pi)/7+cos(6pi)/7`

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CENGAGE ENGLISH-TRIGONOMETRIC FUNCTIONS-All Questions
  1. Prove that tanpi/(16)=sqrt(4+2sqrt(2))-(sqrt(2)+1)

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  2. Solve the equation 2sinx+cosy=2 for the value of xa n dydot

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  3. Find the value of cos(2pi)/7+cos(4pi)/7+cos(6pi)/7

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  4. Prove that sintheta+sin3theta+sin5theta+.....+sin(2n-1)theta=(sin^2nth...

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  5. Prove that (cos3x)/(sin2xsin4x)+(cos5x)/(sin4xsin6x)+(cos7x)/(sin6xsi...

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  6. Prove that 2sin2^0+4sin4^0+6"sin"6^0+.......+180sin180^0=90cot1^0dot

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  7. If A+B+C=180^@, then prove thatcos^2 A + cos^2 B +cos^2 C=1-2cosA cosB...

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  8. Prove that in triangle A B C ,cos^2A+cos^2B-cos^2C=1-2sinAsinBcosCdot

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  9. In triangle ABC, prove that sin(B+C-A)+sin(C+A-B)+sin(A+B-C)=4sin Asi...

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  10. Prove that sum(k=1)^(n-1)(n-k)cos(2kpi)/n=-n/2, wherengeq3 is an int...

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  11. If (tan(ln6)dottan(ln2)dot"tan"(ln3))/(tan(ln6)-tan(ln2)-"tan"(ln3))=k...

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  12. In any triangle A B C ,sin^2A-sin^2B+sin^2C is always equal to (A) 2s...

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  13. If cot^2Acot^2B=3, then the value of (2-cos2A)(2-cos2B) is

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  14. If tanalpha=m/(m+1) and tanbeta=1/(2m+1) . Find the possible values o...

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  15. If u=sqrt(a^2 cos^2 theta + b^2sin^2theta)+sqrt(a^2 sin^2 theta + b^2 ...

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  16. The value of sin^2 12^0+sin^2 21^0+sin^2 39^0+sin^2 48^0-sin^2 9^0-sin...

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  17. The value of f(x)=x^4+4x^3+2x^2-4x+7, when x=cot((11pi)/8) is

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  18. Show that sqrt(3)cosec 20^@ - sec 20^@= 4

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  19. If (1+sint)(1+cost)=5/4 then find the value of (1-sint)(1-cost)dot

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  20. If alpha,beta,gamma,delta are the smallest positive angles in ascendi...

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