Home
Class 12
MATHS
If A= sum (r=1)^(3)"cos"(2r pi)/(7) and...

If `A= sum _(r=1)^(3)"cos"(2r pi)/(7) and B=sum_(r=1)^(3)"cos"(2^(r )pi)/(7)`, then :

A

`A+B=0`

B

`2A+B=0`

C

`A+2B=0`

D

`A=B`

Text Solution

Verified by Experts

The correct Answer is:
D
Promotional Banner

Topper's Solved these Questions

  • COMPOUND ANGLES

    VK JAISWAL ENGLISH|Exercise Exercise-2 : One or More than One Answer is/are Correct|26 Videos

  • COMPOUND ANGLES

    VK JAISWAL ENGLISH|Exercise Exercise-3 : Comprehension Type Problems|12 Videos

  • COMPLEX NUMBERS

    VK JAISWAL ENGLISH|Exercise EXERCISE-5 : SUBJECTIVE TYPE PROBLEMS|8 Videos

  • CONTINUITY, DIFFERENTIABILITY AND DIFFERENTIATION

    VK JAISWAL ENGLISH|Exercise EXERCISE (SUBJECTIVE TYPE PROBLEMS)|22 Videos

Similar Questions

Explore conceptually related problems

Let S= sum_(r=1)^(5) cos (2r-1) (pi)/(11) and P=Pi_(r=1)^(4) cos (2^(r). (pi)/(15)) , then

Evaluate sum_(r=1)^(n-1) cos^(2) ((rpi)/(n)) .

If a = sum_(r=1)^(oo) 1/(r^(2)), b = sum_(r=1)^(oo) 1/((2r-1)^(2)), then (3a)/b is equal to _____

Evaluate: sum_(r=1)^n(3^r-2^r)

If sum_(r=1)^n r=55 , F i nd sum_(r=1)^n r^3dot

sum_(r=1)^10 r/(1-3r^2+r^4)

If S_(n) = sum_(r=1)^(n) (r )/(1.3.5.7"……"(2r+1)) , then

If a=sum_(r=1)^oo 1/r^4 then sum_(r=1)^oo 1/((2r-1)^4)=

sum_(r=1)^(n) r^(2)-sum_(r=1)^(n) sum_(r=1)^(n) is equal to

If sum_(r=0)^(n-1)log_(2)((r+2)/(r+1)) =prod_(r=10)^(99)log_(r) (r+1), then 'n' is equal to (A) 4 (B) 3 (C) 5 (D) 6

VK JAISWAL ENGLISH-COMPOUND ANGLES-Exercise-5 : Subjective Type Problems
  1. If A= sum (r=1)^(3)"cos"(2r pi)/(7) and B=sum(r=1)^(3)"cos"(2^(r )pi)...

    Text Solution

    |

  2. Let P=(sin80^(@)sin65^(@) sin35^(@))/(sin20^(@)+sin50^(@)+sin110^(@))...

    Text Solution

    |

  3. The value of expression (1-cot23^(@))(1-cot22^(@)) is equal to :

    Text Solution

    |

  4. If tanA and tanB the roots of the quadratic equation, 4x^(2)-7x+1=0 th...

    Text Solution

    |

  5. A(1)A(2)A(3)………A(18) is a regular 18 sided polygon. B is an external p...

    Text Solution

    |

  6. If 10sin^(4)alpha+15cos^(4)alpha=6 and the value of 9"cosec"^(4)alpha...

    Text Solution

    |

  7. The value of (1+"tan"(3pi)/(8)"tan"(pi)/(8))+(1+"tan"(5pi)/(8)"tan"(3p...

    Text Solution

    |

  8. If alpha=pi/7 then find the value of (1/cosalpha+(2cosalpha)/(cos2alph...

    Text Solution

    |

  9. Given the for a,b,c,d in R, if a sec(200^@)- ctan(200^@)=d and b sec(...

    Text Solution

    |

  10. The expression 2"cos"(pi)/(17)*"cos"(9pi)/(17)+"cos"(7pi)/(17)+"cos"(9...

    Text Solution

    |

  11. If the expression (sin theta sin2theta+sin3theta sin60theta+sin4theta...

    Text Solution

    |

  12. Let a=sin10^(@), b =sin50^(@), c=sin70^(@)," then " 8abc((a+b)/(c ))((...

    Text Solution

    |

  13. If sin^(3)theta+sin^(3)(theta+(2pi)/(3))+sin^(3)(theta+(4pi)/(3))=a s...

    Text Solution

    |

  14. If sum(r=1)^(n)((tan 2^(r-1))/(cos2^(r )))=tanp^(n)-tan q, then find t...

    Text Solution

    |

  15. If x=sec theta-tan theta and y="cosec"theta+cot theta," then " y-x-xy...

    Text Solution

    |

  16. Prove that: cos18^0-sin18^0 = sqrt(2)sin27^0

    Text Solution

    |

  17. The value of 3(sin1-cos1)^(4)+6(sin1+cos1)^(2)+4(sin^(6)1+cos^(6)1) i...

    Text Solution

    |

  18. If x=alpha satisfy the equation 3^(sin2x+2cos^(2)x)+3^(1-sin2x+2sin^(...

    Text Solution

    |

  19. If y=(sin theta+"cosec" theta)^(2) +(cos theta+sec theta)^(2), then m...

    Text Solution

    |

  20. If tan20^(@)+tan40^(@)+tan80^(@)-tan60^(@)=lambda sin40^(@), then lamb...

    Text Solution

    |

  21. If K^(@) lies between 360^(@) and 540^(@) and K^(@) satisfies the equa...

    Text Solution

    |