Results 1 to 3 of 3

Math Help - proof

  1. #1
    Junior Member
    Joined
    Dec 2005
    Posts
    40

    proof

    i have got the question...

    in triangle ABC, the lengths of the sides a, b, c have the relation 2b equals to a + c.

    i. prove that 2 sin B equals sin A + sin C.
    this part i have done...
    but i can t handle the next part, which is

    ii hence, show that cos {(A - C)/2 } = 2 sin(B / 2)
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member malaygoel's Avatar
    Joined
    May 2006
    From
    India
    Posts
    648
    Quote Originally Posted by ling_c_0202
    i have got the question...

    in triangle ABC, the lengths of the sides a, b, c have the relation 2b equals to a + c.

    i. prove that 2 sin B equals sin A + sin C.
    this part i have done...
    but i can t handle the next part, which is

    ii hence, show that cos {(A - C)/2 } = 2 sin(B / 2)
    2sinB = sinA + sinC
    Use
    sinB =2sin\frac{B}{2}cos\frac{B}{2}
    sinA + sinC = 2sin\frac{A+C}{2}cos\frac{A-C}{2}
    sin\frac{A+C}{2}=sin\frac{\pi - B}{2}=sin\frac{B}{2}
    Keep smiling
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Dec 2005
    Posts
    40

    thank you

    thanks for your reply. however, there is a minor mistake.
    <br />
sin\frac{A+C}{2}=sin\frac{\pi - B}{2}=cos\frac{B}{2}<br />
    but i can still get the answer. thanks a lot
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 5
    Last Post: October 19th 2010, 10:50 AM
  2. Replies: 0
    Last Post: June 29th 2010, 08:48 AM
  3. [SOLVED] direct proof and proof by contradiction
    Posted in the Number Theory Forum
    Replies: 2
    Last Post: February 27th 2010, 10:07 PM
  4. Proof with algebra, and proof by induction (problems)
    Posted in the Discrete Math Forum
    Replies: 8
    Last Post: June 8th 2008, 01:20 PM
  5. proof that the proof that .999_ = 1 is not a proof (version)
    Posted in the Advanced Applied Math Forum
    Replies: 4
    Last Post: April 14th 2008, 04:07 PM

Search Tags


/mathhelpforum @mathhelpforum